Ultrasonic imaging device with programmable anatomy and flow imaging

ABSTRACT

An imaging device includes a transducer that includes an array of piezoelectric elements formed on a substrate. Each piezoelectric element includes at least one membrane suspended from the substrate, at least one bottom electrode disposed on the membrane, at least one piezoelectric layer disposed on the bottom electrode, and at least one top electrode disposed on the at least one piezoelectric layer. Adjacent piezoelectric elements are configured to be isolated acoustically from each other. The device is utilized to measure flow or flow along with imaging anatomy.

BACKGROUND

Transducers in ultrasonic imagers transmit an ultrasonic beam towardsthe target to be imaged and a signal from the reflected waveform is usedto create an image. The reflected waveform from tissue is used to forman image of the anatomy being viewed, whereas blood flow, velocity anddirection of flow is measured using Doppler shift principles underelectronic control.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various examples of the principlesdescribed herein and are part of the specification. The illustratedexamples are given merely for illustration, and do not limit the scopeof the claims.

FIG. 1 illustrates a block diagram of an imaging device for anatomy andflow imaging, according to an example of the principles describedherein.

FIG. 2 illustrates a diagram of a portable imaging system for anatomyand flow imaging, according to an example of the principles describedherein.

FIG. 3 illustrates a schematic diagram of an imaging device with imagingcapability, according to an example of the principles described herein.

FIG. 4 illustrates a side view of a curved transducer array, accordingto an example of the principles described herein.

FIG. 5 illustrates a top view of a transducer, according to an exampleof the principles described herein.

FIG. 6A illustrates an isometric view of an imaging device and scanlines of a frame, according to an example of the principles describedherein.

FIG. 6B illustrates azimuth (xa), elevation (ya) and axial/depth (za)directions.

FIG. 6C illustrates beam focus and steering with changes in delay forelements on a column.

FIG. 6D illustrates a two-dimensional matrix of elements, where relativedelays on columns are changed.

FIG. 7 illustrates the formation of a scan line, according to an exampleof the principles described herein.

FIG. 8 illustrates a flowchart of a method for selectively altering anumber of channels of an imaging device, according to an example of theprinciples described herein.

FIG. 9 illustrates a receive channel, according to an example of theprinciples described herein.

FIG. 10 illustrates a simplified schematic of a low-noise amplifier(LNA) of a receive channel, according to an example of the principlesdescribed herein.

FIG. 11 illustrates a circuit diagram of a fast power-up biasingcircuit, according to an example of the principles described herein.

FIG. 12 illustrates the fabrication of a piezoelectric element,according to an example of the principles described herein.

FIG. 13 illustrates the fabrication of a piezoelectric element,according to an example of the principles described herein.

FIG. 14 illustrates the fabrication of a piezoelectric element,according to an example of the principles described herein.

FIG. 15 illustrates the fabrication of a piezoelectric element,according to an example of the principles described herein.

FIG. 16 illustrates the fabrication of a piezoelectric element,according to an example of the principles described herein.

FIG. 17A illustrates element construction for isolation to reduce crosstalk between neighboring elements.

FIG. 17B illustrates element construction for isolation to reduce crosstalk between neighboring elements.

FIG. 17C illustrates a cross-sectional view of a transducer elementconnected to a corresponding application-specific integrated circuit(ASIC) with at least transmit drivers and receive amplifier electronicsin the ASIC.

FIG. 18 illustrates a top view of a bottom electrode disposed on asubstrate layer and arranged over a membrane, according to an example ofthe principles described herein.

FIG. 19A illustrates a schematic diagram of a piezoelectric element,according to another example of the principles described herein.

FIG. 19B illustrates a symbolic representation of the piezoelectricelement of FIG. 19A, according to an example of the principles describedherein.

FIG. 19C illustrates a cross-sectional view of a piezoelectric element,according to an example of the principles described herein.

FIG. 19D illustrates a cross-sectional view of two sub-elements disposedon a substrate, according to an example of the principles describedherein.

FIG. 19E illustrates a cross-sectional view of two adjacent elementsshowing details of piezo layers, conductors and means of isolation,according to an example of the principles described herein.

FIG. 19F illustrates a cross-sectional view of two adjacent elements,showing isolation details to minimize cross talk, according to anexample of the principles described herein.

FIG. 19G illustrates a cross-sectional view of two adjacent elements,with isolation details to minimize cross talk, according to an exampleof the principles described herein.

FIG. 19H illustrates a cross-sectional view of two adjacent elements,with isolation details to minimize cross talk, according to an exampleof the principles described herein.

FIG. 19I illustrates a piezoelectric element using flexural mode ofoperation, according to an example of the principles described herein.

FIG. 20A illustrates a scan line showing an ensemble of pulses,according to an example of the principles described herein.

FIG. 20B illustrates an imaging frame with multiple scan lines with eachline showing multiple samples, according to an example of the principlesdescribed herein.

FIG. 21 illustrates a transmit and receive operation using sub-elementsand subsets to obtain an image, according to an example of theprinciples described herein.

FIG. 22 illustrates an elevation plane being tilted and focused,according to an example of the principles described herein.

FIG. 23 illustrates an azimuth focus being altered electronically,according to an example of the principles described herein.

FIG. 24 illustrates a flow sensitive region in a Doppler sample volume.

Throughout the drawings, identical reference numbers designate similar,but not necessarily identical, elements. The figures are not necessarilyto scale, and the size of some parts may be exaggerated to more clearlyillustrate the example shown. Moreover, the drawings provide examplesand/or implementations consistent with the description; however, thedescription is not limited to the examples and/or implementationsprovided in the drawings.

DETAILED DESCRIPTION

The present invention relates to imaging devices, and more particularlyto portable handheld ultrasonic imaging devices having the ability toperform flow and anatomy imaging.

Ultrasound imaging (sonography) uses high-frequency sound waves to viewinside the body. Because ultrasound images are captured in real-time,they can also show movement of the body's internal organs as well asblood flowing through the blood vessels. The sound waves are used tocreate and display images of internal body structures such as tendons,muscles, joints, blood vessels, and internal organs.

To perform imaging, the imaging device transmits a signal into the bodyand receives a reflected signal from the body part being imaged. Typesof imaging devices include transducers, which may also be referred to astransceivers or imagers, and which may be based on either photo-acousticor ultrasonic effects. Such transducers can be used for imaging as wellas other applications. For example, transducers can be used in medicalimaging to view anatomy of tissue or other organs in a body. Transducerscan also be used in industrial applications such as materials testing ortherapeutic applications such as local tissue heating of HIFU basedsurgery. When imaging a target and measuring movement of the target,such as flow velocity and direction blood, Doppler measurementstechniques are used. Doppler techniques are also applicable forindustrial applications to measure flow rates, such as fluid or gas flowin pipes.

The difference between transmitted and reflected wave frequencies due torelative motion between the source and the object is known as a Dopplereffect. The frequency shift is proportional to the movement speedbetween the transducer and the object. This effect is exploited inultrasound imaging to determine blood flow velocity and direction.

Doppler imagers may generate either continuous wave (CVV) or a pulsedwave (PW) ultrasound beam. In CW Doppler, signals are continuouslytransmitted and received, requiring two element transducers, one fortransmitting and another for receiving. In PW operation, asingle-element transducer is used for transmitting and receiving theultrasound signals.

For ultrasound imaging, transducers are used to transmit an ultrasonicbeam towards the target to be imaged. A reflected waveform is receivedby the transducer, converted to an electrical signal and with furthersignal processing, an image is created. Velocity and direction of flowmay be measured using an array of micro-machined ultrasonic transducers(MUTs).

B-mode imaging for anatomy is a two-dimensional ultrasound image displaycomposed of dots representing the ultrasound echoes. The brightness ofeach dot is determined by the amplitude of the returned echo signal.This allows for visualization and quantification of anatomicalstructures, as well as for the visualization of diagnostic andtherapeutic procedures. Usually, the B-mode image bears a closeresemblance to the actual anatomy of a cutout view in the same plane. InB-mode imaging, a transducer is first placed in a transmit mode and thenplaced in receive mode to receive echoes from the target. The echoes aresignal processed into anatomy images. The transducer elements areprogrammable such that they can be either in transmit mode or in receivemode, but not simultaneously.

The use of color flow Doppler, color Doppler imaging, or simply colorDoppler allows the visualization of flow direction and velocity forblood in an artery or vein within a user defined area. A region ofinterest is defined, and the Doppler shifts of returning ultrasoundwaves are color-coded based on average velocity and direction. Sometimesthese images are overlapped (co-imaged) with anatomy images in B-modescan to present a more intuitive feel of flow relative to anatomy beingviewed. Doppler imaging can also be PW Doppler so that the range andvelocity of flow is determined, but maximum flow rate is dependent onpulse repetition frequency used, otherwise images are aliased makinghigher velocities look like lower velocities. Doppler shift can bemeasured from an ensemble of waves received to measure flow velocityusing PW mode of Doppler imaging. CW Doppler is a continuous imagingtechnique where aliasing is avoided through continuous transmitting fromone transducer element while receiving echoes from another transducerelement. With this technique, the range is ambiguous. In a programmableinstrument, both pulsed and continuous techniques can be implemented asdiscussed later. PW and Color Doppler may use a selected number ofelements in an array. First, the elements are placed in a transmit modeand after echoes have returned, the elements are placed in a receivemode where the received signal is processed for Doppler signal imaging.For CW Doppler, at least two different elements are utilized, where eachelement is in transmit mode while the other element is in receive modecontinuously.

The Doppler signal from a moving object contains not only informationabout flow, but also backscatter signals containing clutter thatoriginates from surrounding tissue or slowly moving vessels. Thisclutter signal may be typically 40 to 80 dB stronger than the Dopplershift signal originating from blood. Thus, a clutter rejection is neededto estimate the flow accurately. Clutter suppression is a step in theprocessing of Doppler signal. A high pass filter (HPF) may be used toremove the clutter signal from the Doppler shift signal. A high passfilter is used to suppress signals from stationary or slow-moving tissueor any other organs. Signals from slow moving objects are oflow-frequency, but they may have amplitudes much stronger than highfrequency signals generated from the faster blood flow. Thus, forseparating the signals from blood and tissue, a high pass filter with asharp transition band is used. These filters can be developed digitallyin the receiver. These filters, sometimes known as Wall filters, look atthe difference in signals from different transmissions, with the signalsaligned in phase. Any deviation caused by Doppler shift is the desiredoutput. However, if low frequency clutter causes some of this deviation,the sensitivity of the flow detection algorithm becomes degraded.Effects from switched mode dc to dc converter-based power supplies maycause clock frequency and harmonics to show up in the power supply.Further, these frequencies can create other frequencies due tointeraction of other switching phenomena, for example, pulse repetitionrate of the Doppler sequence.

To the extent that these kinds of behavior or intermodulation behaviorare caused by nonlinearities, spurious signals show up in thefrequencies of interest for flow imaging and sensitivity of flow imagingis reduced. Another example of clutter is amplitude jitter of the pulsesused in the transmit pulsar. One source of the clutter may be the powersupply amplitudes varying from pulse to pulse, due to the power supplycapacitors being drained of charge to deliver current during a pulse andnot getting recharged to a same level for the next pulse.

In addition to use of digital Wall filters, low frequency contentcausing clutter can be minimized by using a high pass filter ahead ofthe digital filter. Filters can be in the analog domain and also in thedigital domain. A part of these filters can also be performed right atthe transducer interface, where real time control of high pass frequencyis achieved by controlling the radio frequency (R_(f)) and carrierfrequency (C_(HF)) network. Radio frequency (R_(f)) refers to the rateof oscillation of electromagnetic radio waves in the range of 3 kHz to300 GHz, as well as the alternating currents carrying the radio signals.Carrier frequency (C_(HF)) is defined as the transmission of a fixedfrequency that has been altered or otherwise modulated to carry data.This achieves a 20 dB/Dec high pass slope.

Additionally, beyond use of a low noise amplifier (LNA), other digitallycontrolled high pass filters (HPF) can be leveraged to simplifyoperations in the receiver to save power and processing time. Byrejecting unneeded clutter before time gain compensation (TGC), an LNAincreases the dynamic range of the signal presented to an analog todigital converter (ADC). The digitized bits can now be processed forfurther Doppler operations.

The acquisition of Doppler relies on repeated transmission of pulses toacquire data from a particular region of interest. Such acquisition isprecise in its periodicity to ensure that the Doppler signal isuniformly sampled for further spectrogram processing. This can be amajor constraint to ultrasound imaging systems when this Doppler signalacquisition is done in such modes as Duplex or Triplex imaging whereB-mode or color flow signals are acquired concurrently. This constraintreduces the frame rates for other modes and hence limits the ability ofthe sonographer to follow events in real-time. Moreover, the rapidperiodic transmission of ultrasound pulses to the same location canincrease the average power per unit area beyond certain safety standardsand therefore limitations on acoustic power generated drive closeattention to keep this in the safe zone.

Doppler shift principles are used to calculate the blood flow velocity.Other types of velocity can be calculated, such as body fluids,industrial fluids, gases, etc. When the observer moves towards thesource, the increased frequency, f_(r), due to passing more wave cyclesper seconds, is given by:

$f_{r} = {f_{t}\frac{c + v}{c}}$

In the above, f_(t) is the transmitted frequency, c is the velocity ofsound in tissue, and v is the velocity of the observer (for example,blood).

The velocity is replaced by the component of velocity in the wavedirection, v cos ø, if the velocity of the observer is at an angle ø tothe direction of the wave propagation.

${f_{ry} = f_{t}}\frac{c + {v\;\cos\;\varnothing}}{c}$

If the observer is at rest and the source moves with the velocity in thedirection of wave travel, the wavelengths are compressed. The resultingobserved frequency is:

$f_{ry} = {f_{t}\frac{c}{c - \nu}}$

Taking the angle into account:

$f_{ry} = {f_{t}\frac{c}{c - {v\;\cos\;\varnothing}}}$

In application of ultrasound, an ultrasonic beam is backscattered fromthe moving blood cells and tissue. Both of the above effects combine togive the transmitted Doppler shift in frequency. The observed frequencyis then given by:

$f_{ry} = {{f_{t}\frac{c + {\nu\;\cos\;\varnothing}}{c}*\frac{c}{c - {\nu\cos\;\varnothing}}} = {f_{t}\frac{c + {\nu\cos\;\varnothing}}{c - {\nu\cos\;\varnothing}}}}$

As mentioned, the Doppler shift frequency is the difference betweenincident frequency f_(t) and reflected frequency f_(r), and is thereforegiven by:

f_(d) = f_(r−)f_(t)$f_{d} = {{f_{t}\frac{c + {\nu\cos\;\varnothing}}{c - {\nu\cos\;\varnothing}}} - f_{t}}$

Since c>>v

$f_{d} = {\frac{2*{ft}*\nu}{c}\cos\;\varnothing}$

From the last relationship, the Doppler shift depends on the angle θ tothe direction of the propagation and the transmitted frequency.

The best reflection takes place when measuring at 90 degrees to theelectronically steered in the azimuth and elevation plane to achieveoptimal Doppler signal detection. This elevation steering is controlledby a combination of elevation delay control along with any desiredazimuth.

A continuous wave Doppler system is a system that sends and receives acontinuous ultrasound wave by using two separate transducer elementshoused within the same probe. Because transmission and reception arecontinuous, the system has no depth resolution, except in the sense thatsignals originating from close to the transducer experience lessattenuation than those from a distant target. The transmitted 2112 andreceived beams 2114 are shown in a Doppler sample volume in FIG. 24. Theflow sensitive zone 2116 over which Doppler information can be acquired(sample volume) is the region of transmitting and receiving beam overlapas indicated by cross-hatched lines that occur at some distance from thetransducer face.

It is possible to construct an element that includes two sub-elementsfor example, where one can be in transmit mode and the other in receivemode. By using embedded dual sub-elements instead of a single element inthe transducer, the entire transducer area or portions selected thereofcan be used for transmission and reception. Also, areas of intersectionare increased by use of dual sub-elements.

Imaging devices such as ultrasound imagers used in medical imaging usepiezoelectric (PZT) material or other piezo ceramic and polymercomposites. To fabricate the bulk PZT elements for the transducers, athick piezoelectric material slab can be cut into large rectangularshaped PZT elements. The rectangular-shaped PZT elements are expensiveto build, since the manufacturing process involves precise cutting ofthe rectangular-shaped thick PZT or ceramic material and mounting itonto substrates with precise spacing. Furthermore, the impedance of thetransducers is much higher than acoustic impedance of tissue, whichrequires use of impedance matching layers to allow for practicaltransmission and reception of signals.

Still further, such thick bulk PZT elements can require relatively highvoltage pulses. For example, 100 volts (V) or more may be required togenerate transmission signals. High drive voltage results in high powerdissipation since the power dissipation in the transducers isproportional to the square of the drive voltage. The high powerdissipation generates heat within the imaging device such that coolingarrangements are necessitated. The use of cooling systems increases themanufacturing costs and weights of imaging devices which makes theimaging devices more burdensome to operate. High voltages also increasethe cost of electronics.

Even further, the transmit/receive electronics for the transducers maybe located far away from the transducers themselves, thus requiringmicro-coaxial cables between the transducers and transmit/receiveelectronics. In general, the cables have a precise length for delay andimpedance matching, and, quite often, additional impedance matchingnetworks are used for efficient connection of the transducers throughthe cables to the electronics.

Accordingly, the present specification describes the use ofpiezoelectric micromachined ultrasound transducers (pMUTs), which can beefficiently formed on a substrate leveraging various semiconductor wafermanufacturing operations. Semiconductor wafers may come in 6 inch, 8inch, and 12 inch sizes and are capable of housing hundreds oftransducer arrays. These semiconductor wafers start as a siliconsubstrate on which various processing steps are performed. An example ofsuch an operation is the formation of SiO2 layers, also known asinsulating oxides. Various other steps such as the addition of metallayers to serve as interconnects and bond pads or copper pillars may beused to allow connections of the pMUTs to other electronics. Also, useof etching techniques to create cavities in the silicon structure allowsformation of membranes that can move under electrical control or due toexternal pressure inputs. Compared to the conventional transducershaving bulky piezoelectric material, pMUTs built on semiconductorsubstrates are less bulky, are cheaper to manufacture, and have simplerand higher performance interconnection between electronics andtransducers. As such, they provide flexibility in the operationalfrequency, and potential to generate higher quality images due to lowerparasitics in the interconnection.

In one example, the imaging device is coupled to an application specificintegrated circuit (ASIC) that includes transmit drivers, sensingcircuitry for received echo signals, and control circuitry to controlvarious operations. The ASIC can be formed on a separate semiconductorwafer and the pMUT on another wafer. Also, the ASIC can be placed inclose proximity to pMUT elements to reduce parasitic losses. In oneexample, the ASIC may be 50 micrometers (μm) or less away from thetransducer array. There may be less than a 100 μm separation between the2 wafers or 2 die, where each wafer includes many dies and a dieincludes a transducer in the transducer wafer and an ASIC in the ASICwafer. The ASIC may have matching dimensions relative to the pMUT toallow the devices to be stacked for wafer-to-wafer interconnection ortransducer die on ASIC wafer or transducer die to ASIC dieinterconnection. Alternatively, the transducer can be developed on topof the ASIC wafer using low temperature piezo material sputtering andother low temperature processing compatible with ASIC processing.

While pMUTs have potential for advanced ultrasonic imaging, somelimitations have impeded their utilization in high performance imagingimplementation. As an example, pMUTs utilizing Aluminum Nitride exhibitlow sensitivity related to transmit and receive operations making themcandidates for less demanding applications. Other pMUTs utilizing PZTrequire relatively high voltages and exhibit relatively low bandwidthand low efficiency.

Accordingly, the present specification describes pMUTs that 1) have anenhanced sensitivity, 2) may operate at low voltages, 3) exhibit highbandwidth operation, and 4) exhibit good linearity. Specifically, thepresent specification describes pMUTs in close proximity to theassociated control circuitry. This allows 2D and 3D imaging undercontrol of a control circuitry in a small portable device.

Another type of transducer is a capacitive micromachine ultrasonictransducer (cMUT). However, cMUT sensors have difficulty with generatingsufficient acoustic pressure at lower frequencies (where the bulk ofdeep medical imaging occurs) compared to PZT based devices and areinherently nonlinear. Furthermore, cMUTs require high voltage operation.

In general, an imaging device of the present specification includes anumber of transmit channels and a number of receive channels. Transmitchannels drive the piezoelectric elements with a voltage pulse at afrequency the elements are responsive to. This causes an ultrasonicwaveform to be emitted from the piezoelectric elements which waveform isdirected towards an object to be imaged. In some examples, the imagingdevice with the transducer array of piezoelectric elements makesmechanical contact with the body using a gel in between the imagingdevice and the body. The ultrasonic waveform travels towards the object,i.e., an organ, and a portion of the waveform is reflected back to thepiezoelectric elements, where the received ultrasonic energy isconverted to an electrical energy, which is then further processed by anumber of receive channels and other circuitry to develop an image ofthe object.

These transmit and receive channels consume power and in instrumentswhere there are many channels (to generate high quality images), thepower may cause excessive heat buildup in the imaging device. If thetemperature rises past a certain value, it may affect operation of theimaging device, could pose a danger to the operator, could pose a dangerto a patient, and may be outside of regulatory specifications whichrestrict how high the temperature can rise. An ultrasound imaging deviceincludes a transducer array, an ASIC, transmit and receive beamformingcircuitry, and control electronics. Specifications restrict the maximumtemperature that can be tolerated, which in turn, severely restrictswhich electronic circuits can be housed in the imaging device and alsorestricts how the imaging device is operated. Such restrictions cannegatively affect the image quality achieved and the frame rate ofimages. Furthermore, imaging devices may be battery-powered which maydrain quickly in instruments with many channels as each channel drawsenergy.

The imaging device of the present disclosure resolves these and otherissues. Specifically, the imaging device controls power dissipationwithout exceeding temperature limits of the imaging device all whilemaintaining needed image quality. Specifically, the number of receivechannels and/or transmit channels used to form an image areelectronically adaptable to save power, for example, in cases where alower number of channels is acceptable. As a specific example, each ofthe number of channels may be dynamically controlled to reduce power, orto be powered down entirely. Additionally, other characteristics of eachchannel are also configurable to reduce power. Such advanced controlallows the imaging device to be operated within safe temperaturethresholds, and may do so without materially sacrificing needed imagequality. The lower power consumption also increases battery life.

Also, the imaging device includes a handheld casing where transducersand associated electronics are housed. The imaging device may alsocontain a battery to power the electronics. As described above, theamount of power consumed by the imaging device increases the temperatureof the imaging device. To ensure satisfactory use of the imaging deviceand imaging device performance, the temperature of the body of theimaging device should remain below a threshold temperature. The imagingdevice of the present specification is electronically configured toreduce power and temperature notwithstanding the acquisition of highquality images which consumes a significant amount of power, reducesbattery life, and increases temperature in the probe.

In one example, the present disclosure describes a high performance, lowpower, and low cost portable imaging device capable of 2D and 3D imagingusing pMUTs in a 2D array built on a silicon wafer. Such an arraycoupled to an ASIC with electronic configuration of certain parametersenables a higher quality of image processing at a lower cost than hasbeen previously possible. By controlling certain parameters, such as thenumber of channels used or the amount of power used per channel, powerconsumption can be altered and temperature can be changed.

The present disclosure describes an imaging device that relies onpMUT-based transducers connected to control electronics on a per pixelbasis and housed in a portable housing. The imaging device allows systemconfigurability and adaptability in real time to actively control powerconsumption and temperature in the imaging device. Flow imaging, inparticular, can consume more power than anatomy imaging modes. Power isreduced by minimizing power dissipation within the imaging device by 1)altering the aperture size and/or 2) actively controlling powerdissipation in those channels such that temperatures within the imagingdevice do not exceed specification limits. All this is done whileachieving superior performance than would otherwise be possible.Further, acoustic power output can increase in Doppler modes compared toother anatomy modes. Electronic means are provided to control such poweroutput levels.

The manufacturing cost of pMUTs described herein may be reduced byapplying modern semiconductor and wafer processing techniques. Forexample, a thin film piezoelectric layer may be spun on or sputteredonto semiconductor wafers and later patterned to create piezoelectricsensors that each have two or more electrodes. In one example, eachpiezoelectric element may be designed to have the ability to emit orreceive signals at a certain frequency, known as the center frequency,as well as the second and/or additional frequencies. Note that the termpiezoelectric element, pMUT, transceiver, and pixel are used hereininterchangeably.

In one example, an imaging device includes a transducer that has anarray of piezoelectric elements that are formed on a substrate. Each ofthe piezoelectric elements include at least one membrane suspended fromthe substrate, at least one bottom electrode disposed on the membrane,at least one piezoelectric layer disposed on the bottom electrode, andat least one top electrode disposed on the at least one piezoelectriclayer. Adjacent piezoelectric elements are configured to be isolatedacoustically from each other.

In another example, an imaging device includes a transducer with atwo-dimensional (2D) array of piezoelectric elements arranged in rowsand columns on the transducer. Each piezoelectric element has at leasttwo terminals and is physically isolated from each adjacentpiezoelectric element to minimize cross talk. A first set ofpiezoelectric elements of the array includes that each piezoelectricelement has a first top electrode connected to a respective receiveamplifier and is electronically programmed as if connected together toform a first column. A second set of piezoelectric elements of the arrayincludes that each piezoelectric element has a second top electrodeconnected to a respective transmit driver and is electronicallyprogrammed as if connected together to form a second column.

In another example, an imaging device includes a transducer and a 2Darray of piezoelectric elements arranged in rows and columns on thetransducer. Each piezoelectric element has at least two terminals. Atleast a first column of the piezoelectric elements includes that eachpiezoelectric element has a first top electrode connected to arespective receive amplifier or a transmit driver under programmedcontrol. At least a second column of the piezoelectric elements includesthat each piezoelectric element has a first top electrode connected to arespective receive amplifier or transmit driver under programmedcontrol. The piezoelectric elements are programmed to transmit and thensubsequently receive or to simultaneously transmit and receive.

Turning now to the figures, FIG. 1 illustrates a block diagram of animaging device (100) with transmit (106) and receive channels (108),controlled by control circuitry (109), and having imaging computationsperformed on a computing device (110) according to principles describedherein. FIG. 1 further includes a power supply (111) to energize thevarious components in the imaging device (100).

As described above, the imaging device (100) may be used to generate animage of internal tissue, bones, blood flow, or organs of human oranimal bodies. Accordingly, the imaging device (100) transmits a signalinto the body and receives a reflected signal from the body part beingimaged. Such imaging devices (100) include piezoelectric transducers(102), which may be referred to as transceivers or imagers, which may bebased on photo-acoustic or ultrasonic effects. The imaging device (100)can be used to image other objects as well. For example, the imagingdevice (100) can be used in medical imaging, flow measurements forfluids or gases in pipes, lithotripsy, and localized tissue heating fortherapeutic and highly intensive focused ultrasound (HIFU) surgery.

In addition to use with human patients, the imaging device (100) may beused to get an image of internal organs of an animal as well. Moreover,in addition to imaging internal organs, the imaging device (100) mayalso be used to determine direction and velocity of blood flow inarteries and veins, as well as tissue stiffness, with Doppler modeimaging.

The imaging device (100) may be used to perform different types ofimaging. For example, the imaging device (100) may be used to performone dimensional imaging, also known as A-Scan, 2D imaging, also known asB scan (B-mode), three dimensional (3D) imaging, also known as C scan,and Doppler imaging. The imaging device (100) may be switched todifferent imaging modes and electronically configured under programcontrol.

To facilitate such imaging, the imaging device (100) includes an arrayof piezoelectric transducers (102), each piezoelectric transducer (102)including an array of piezoelectric elements (104). A piezoelectricelement (104) may also include two of more sub-elements, each of whichmay be configurable in a transmit or receive operation. Thepiezoelectric elements (104) operate to 1) generate the pressure wavesthat are passed through the body or other mass and 2) receive reflectedwaves off the object within the body, or other mass, to be imaged.

In some examples, the imaging device (100) may be configured tosimultaneously transmit and receive ultrasonic waveforms. For example,certain piezoelectric elements (104) may send pressure waves toward thetarget object being imaged while other piezoelectric elements (104)receive the pressure waves reflected from the target object and developelectrical charges in response to the received waves.

In some examples, each piezoelectric element (104) may emit or receivesignals at a certain frequency, known as a center frequency, as well asthe second and/or additional frequencies. Such multi-frequencypiezoelectric elements (104) may be referred to as multi-modalpiezoelectric elements (104) and can expand the bandwidth of the imagingdevice (100).

The piezoelectric material that forms the piezoelectric elements (104)contracts and expands when different voltage values at a certainfrequency are applied. Accordingly, as voltages alternate betweendifferent values applied, the piezoelectric elements (104) transform theelectrical energy (i.e., voltages) into mechanical movements resultingin acoustic energy which is emitted as waves at the desired frequencies.These waves are reflected from a target being imaged and are received atthe same piezoelectric elements (104) and converted into electricalsignals that are then used to form an image of the target.

To generate the pressure waves, the imaging device (100) includes anumber of transmit channels (106) and a number of receive channels(108). The transmit channels (106) include a number of components thatdrive the transducer (102), (i.e., the array of piezoelectric elements(104)), with a voltage pulse at a frequency that they are responsive to.This causes an ultrasonic waveform to be emitted from the piezoelectricelements (104) towards an object to be imaged. The ultrasonic waveformtravels towards the object to be imaged and a portion of the waveform isreflected back to the transducer (102), where the receive channels (108)collect the reflected waveform, convert it to an electrical energy, andprocess it, for example, at the computing device (110), to develop animage that can be displayed.

In some examples, while the number of transmit channels (106) andreceive channels (108) in the imaging device (100) remain constant, thenumber of piezoelectric elements (104) that they are coupled to mayvary. This coupling is controlled by the control circuitry (109). Insome examples, a portion of the control circuitry (109) may bedistributed in the transmit channels (106) and in the receive channels(108). For example, the piezoelectric elements (104) of a transducer(102) may be formed into a 2D array with N columns and M rows.

In one example, the 2D array of piezoelectric elements (104) have anumber of columns and rows, such as 128 columns and 32 rows. The imagingdevice (100) may have up to 128 transmit channels (106) and up to 128receive channels (108). Each transmit channel (106) and receive channel(108) is coupled to multiple or single piezoelectric elements orsub-elements (104). Depending on the imaging mode, each column ofpiezoelectric elements (104) may be coupled to a single transmit channel(106) and a single receive channel (108). The transmit channel (106) andreceive channel (108) receive composite signals, which composite signalscombine signals received at each piezoelectric element (104) within therespective column.

In another example, (i.e., during a different imaging mode), individualpiezoelectric elements (104) are coupled to their own transmit channel(106) and their own receive channel (108).

In other examples, the computing device 110 or power supply and battery111 are external.

FIG. 2 is a diagram of an imaging system with flow imaging capabilityalong with anatomy imaging capability, according to an example of theprinciples described herein. As depicted, the imaging system includesthe imaging device (100) that generates and transmits, via the transmitchannels (FIG. 1, 106) pressure waves (210) toward an internal organ,such as a heart (214), in a transmit mode/process. The internal organ,or other object to be imaged, may reflect a portion of the pressurewaves (210) toward the imaging device (100) which captures, via thetransducer (FIG. 1,102), receive channels (FIG. 1, 108), controlcircuitry (FIG. 1, 109), the computing device (FIG. 1,110), and thereflected pressure waves, and generates electrical signals in a receivemode/process. The system also includes another computing device (216)that communicates with the imaging device (100) through a communicationchannel (218). The imaging device (100) may communicate electricalsignals to the computing device (216) which processes the receivedsignals to complete formation of an image of the object. A displaydevice (220) of the system can then display images of the organ ortarget including images that show blood flow related images in thetargeted areas.

As depicted in FIG. 2, the imaging device (100) may be a portable,handheld device that communicates signals through the communicationchannel (218), either wirelessly (using a protocol, such as 802.11protocol) or via a cable (such as universal serial bus 2 (USB2), USB 3,USB 3.1, and USB-C), with the computing device (216). In the case of atethered connection, the imaging device (100) may include a port asdepicted in FIG. 3 for receiving the cable that is to communicate withthe computing device (216). In the case of a wireless connect, theimaging device (100) includes a wireless transmitter to communicate withthe computing device (216).

The display device (220) and the computing device (216) may be separatefrom the imaging device (100) as shown. For example, the computingdevice (216) and display device (220) may be disposed within a separatedevice (e.g., a mobile device, such as cell phone or iPad, or astationary computing device), which can display images to a user. Inanother example, the display device (220) and the computing device (220)are contained within the imaging device (100). That is, the imagingdevice (100), computing device (216), and display device (220) aredisposed within a single housing.

FIG. 3 is a schematic diagram of an imaging device (100) with flow andanatomy measurement capability, according to an example of theprinciples described herein. As described above, the imaging device(100) may be an ultrasonic medical probe. FIG. 3 depicts thetransducer(s) (102) of the imaging device (100). As described above, thetransducer(s) (102) include an array of piezoelectric elements (FIG. 1,104) that transmit and receive pressure waves (FIG. 2, 210). In someexamples, the imaging device (100) includes a coating layer (322) thatserves as an impedance matching interface between the transducers (102)and the human body, or other mass through which the pressure waves (FIG.2, 210) are transmitted. In some cases, the coating layer (322) mayserve as an impedance matching layer and also a lens when designed witha curvature consistent with a desired focal length. The coating layer(322) may consist of several layers of materials, some of which are usedfor impedance matching the transducer to tissue acoustic impedance andsome of which are shaped into a mechanical lens to focus the acousticsignals in the elevation direction.

In embodiments, the user may apply gel on the skin of the human bodybefore a direct contact with the coating layer (322) so that theimpedance matching at the interface between the coating layer (322) andthe human body may be improved. Impedance matching reduces the loss ofthe pressure waves (FIG. 2, 210) at the interface and the loss of thereflected wave traveling toward the imaging device (100) at theinterface.

In some examples, the coating layer (322) may be a flat layer tomaximize transmission of acoustic signals from the transducer(s) (102)to the body and vice versa. Certain parts of the coating layer (322) maybe a quarter wavelength in thickness at a certain frequency of thepressure wave (FIG. 2, 210) generated or received by the transducer(s)(102).

The imaging device also includes control circuitry (109), such as anASIC, for controlling the transducers (102). The control circuitry (109)may be housed in an ASIC along with other circuitry which is coupled tothe transducers (102) by bumps that connect transducers (102) to theASIC. As described above, the transmit channels (106) and receivechannels (108) may be selectively alterable meaning that the quantity oftransmit channels (106) and receive channels (108) that are active at agiven time may be altered such that the power consumptioncharacteristics of the transmit channels (106) and receive channels(108) and functionality may be altered. For example, if it is desired toalter the acoustic power during flow imaging modes, it is achieved byelectronically controlling transmit channels with respect to the numberof elements to be used on a line or the aperture to be used.

The transmit driving signal may be a multilevel signal, for example, 5V,0V, and −5V. Other examples include 15V, 0V, and −15V. Other values arealso possible. The signal can include many pulses or be continuous at adesired frequency. Drivers at the transmitter convert these multilevelsignals, which are initially encoded into digital binary bits, to thefinal output level, such as say 15V. Using many such channels,ultrasonic transmit beams are created. By controlling delays in thechannels, the beams can be steered in two-dimensional orthree-dimensional domains. With the various beamforming operationsdescribed herein, 3D beamforming is possible. This is enabled using a 2Darray that is addressable in the X and Y axis. Also possible is biplaneimaging.

The imaging device (100) may further include Field Programmable GateArrays (FPGAs) or Graphical Processing Units (GPUs) (326) forcontrolling the components of the imaging device (100); circuit(s)(328), such as Analog Front End (AFE), for processing/conditioningsignals and an acoustic absorber layer (330) for absorbing waves thatare generated by the transducers (102) and propagated towards thecircuits (328). For use with an acoustic absorber layer (330), thetransducer(s) (102) may be mounted on a substrate and may be attached toan acoustic absorber layer (330). This layer absorbs any ultrasonicsignals that are emitted in the reverse direction, which may otherwisebe reflected and interfere with the quality of the image. While FIG. 3depicts the acoustic absorber layer (330), this component may be omittedin cases where other components prevent a material transmission ofultrasound in the backwards direction, i.e., away from the transducers(102). The acoustic absorber may also be embedded between 102 and 109.

The imaging device (100) may include a communication unit (332) forcommunicating data with an external device, such as the computing anddisplay device such as a smart phone or tablet (FIG. 2, 216).Communication may be through a port (334) or a wireless transmitter, forexample. The imaging device (100) may include memory (336) for storingdata. In some examples, the imaging device (100) includes a battery(338) for providing electrical power to the components of the imagingdevice (100). Electronic control of the channels and associatedcircuitry may have a particularly relevant impact when the imagingdevice (100) includes a battery (338). For example, as the receivechannels (FIG. 1, 108) and transmit channels (FIG. 1, 106) includecomponents that draw power, the battery depletes over time. Theconsumption of power by these components in some examples may be ratherlarge such that the battery (338) would drain in a short amount of time.This is particularly relevant when obtaining high quality images whichconsume significant amounts of power. The battery (338) may also includebattery charging circuits which may be wireless or wired chargingcircuits. The imaging device (100) may include a gauge that indicates abattery charge consumed and is used to configure the imaging device(100) to optimize power management for improved battery life.

By reducing the power consumption, or in some examples, powering downcompletely the different channels (FIG. 1, 106, 108), the battery (338)life is extended which enhances the ease of use of the imaging device(100). This is particularly applicable for imagers that support flowimaging, where power consumption is further increased.

FIG. 4 is a side view of a transducer (102) array, according to anexample of the principles described herein. As described above, theimaging device (FIG. 1, 100) may include an array of transducers (102-1,102-2, 102-3), each with their own array of piezoelectric elements (FIG.1, 104). In some examples, the transducers (102) may be curved so as toprovide a wider angle of the object (FIG. 2, 214) to be imaged. In otherexamples, the transducer (102) and arrays are disposed on a flatsurface. FIG. 5 depicts a top view of a transducer (102) array. Asdepicted in FIG. 5, the transducer (102) may include a transceiversubstrate (540) and one or more piezoelectric elements (104) arrangedthereon. Unlike the conventional systems that use bulk piezoelectricelements, the piezoelectric element (104) may be formed on a wafer. Thewafer may be diced to form multiple transducer (102) arrays to be usedto build imaging devices. This process may reduce the manufacturing costsince multiple transducer (102) arrays in dice form may be fabricated inhigh volume and at low cost.

In some examples, the diameter of the wafer may range between 6-12inches and many transducer (102) arrays may be batch manufacturedthereon. Furthermore, in some examples, the control circuitry (FIG. 1,109) for controlling the piezoelectric elements (104) may be formed suchthat each piezoelectric element (104) is connected to the matchingintegrated circuits, (e.g., receive channels (FIG. 1, 108) and transmitchannels (FIG. 1, 106)) in close proximity, preferably within 25 μm-100μm. For example, the transducer (102) may have 1,024 piezoelectricelements (104) and be connected to matching control circuitry (FIG. 1,109) that has the appropriate number of transmit and receive circuitsfor the 1,024 piezoelectric elements (104).

Each piezoelectric element (104) may have any suitable shape such assquare, rectangle, and circle. As depicted in FIG. 5, in some examples,the piezoelectric elements (104) may be arranged in a two-dimensionalarray arranged in orthogonal directions. That is, the piezoelectricelement (104) array may be an M×N array with N columns (542) and M rows(544).

To create a line element, a column (542) of N piezoelectric elements(104) may be effectively connected electronically. Then, this lineelement may provide transmission and reception of ultrasonic signalssimilar to those achieved by a single bulk piezoelectric element, whereeach of both electrodes for each piezoelectric element (104) areelectronically connected to realize a column that is N times larger thaneach piezoelectric element (104). This line element may be called acolumn or line or line element interchangeably. An example of a columnof piezoelectric elements (104) is shown in FIG. 5 by the referencenumber (542). Piezoelectric elements (104) are arranged in a column(542) in this example and have associated transmit driver circuits (partof transmit channel) and low noise amplifiers (LNAs) which are part ofthe receive channel circuitry. Although not explicitly shown, thetransmit and receive circuitry include multiplexing and address controlcircuitry to enable specific elements and sets of elements to be used.It is understood that transducers (102) may be arranged in other shapessuch as circles, or other shapes. In some examples, piezoelectricelements (104) may be spaced 250 μm apart from each other, from centerto center. It should be noted that since the piezoelectric elements(104) are connected under programmed control, the number ofpiezoelectric elements (104) connected in a column, for example, isprogrammable.

For the transducer (102), a line element may be designed using aplurality of identical piezoelectric elements (104), where eachpiezoelectric element (104) may have its characteristic centerfrequency. When a plurality of the piezoelectric elements (104) areconnected together, the composite structure (i.e. the line element) mayact as a line element with a center frequency that consists of thecenter frequencies of all the element pixels. Using modern semiconductorprocesses used to match transistors, these center frequencies match wellto each other and have a very small deviation from the center frequencyof the line element. It is also possible to mix several pixels ofsomewhat different center frequencies to create a wide bandwidth linecompared to lines using only one central frequency.

In some examples, the ASIC that is connected to transducers (102) mayinclude one or more temperature sensors (546-1, 546-2, 546-3, 546-4) tomeasure the temperature in that region of the ASIC and transducer. WhileFIG. 5 depicts temperature sensors (546) disposed at particularlocations, the temperature sensors (546) may be disposed at otherlocations and additional sensors may be disposed at other locations onthe imaging device (FIG. 1, 100).

The temperature sensors (546) may be a trigger to the selectiveadjustment of channels (FIG. 1, 106, 108). That is, as described above,temperatures within a handheld portable imaging device (FIG. 1, 100) mayrise above a predetermined temperature. The transducers (102) may becoated with a material to act as an interface between the transducer andthe patient contact surface. In an example, the material serves as abacking layer disposed on a surface of the transducer facing the ASIC.The material may be a polydimethylsiloxane (PDMS), or other similarmaterial, having an acoustic impedance that is in between the transducerand the tissue acoustic impedance levels for the frequencies ofinterest. The temperature sensors (546) detect a temperature of thedevice at a surface of the imager contacting the patient due toproximity to that area. If the temperature sensors (546) detect atemperature greater than a threshold amount, for example, auser-established temperature or a temperature set by a regulatoryauthority, a signal may be passed by the controller (FIG. 3, 324) topower down all or some of the transmit channels (FIG. 1, 106) and/orreceive channels (FIG. 1, 108) or to set all or some of the transmitchannels (FIG. 1, 106) and/or receive channels (FIG. 1, 108) in a lowpower state.

FIG. 5 also depicts the terminals of the piezoelectric elements (104).Particularly, each piezoelectric element (104) has two terminals. Afirst terminal is a common terminal shared by all piezoelectric elements(104) in the array. The second terminal connects the piezoelectricelements (104) to the transmit channels (FIG. 1, 106) and receivechannels (FIG. 1, 108), where the transmit and receive channels may beon a different substrate. The second terminal is the terminal that isdriven and sensed for every piezoelectric element (104) as shownsymbolically for those piezoelectric elements (104) in the first column.For simplicity the transmit channels (106) and the receive channels(FIG. 1, 108) appear to be connected together. However, in someexamples, they may be separately controlled to be active in transmitmode, in receive mode, or both operations, with wiring being morecomplex than shown here for simplicity. Also, for simplicity, the secondterminal is only indicated for those piezoelectric elements (104) in thefirst column. However, similar terminals with the associated transmitchannels (106) and receive channels (108) populate the otherpiezoelectric elements (104) in the array. The control circuitry (FIG.1, 109), using control signals, may select a column (542) ofpiezoelectric elements (104) by turning on respective transmit channels(FIG. 1, 106) and receive channels (FIG. 1, 108) and turning off thechannels (FIG. 1, 106, 108) in other columns (542). In a similar manner,it is also possible to turn off particular rows (54), or even individualpiezoelectric elements (104).

FIG. 6A is an isometric view of an imaging device (100) and scan lines(650) of a frame (648), according to an example of the principlesdescribed herein. A frame (648) refers to a single still image of anorgan, or other object to be imaged. The frame (648) may be across-sectional line through the object. A frame (648) is made up ofindividual scan lines (650). That is, a frame (648) may be viewed as animage, and a scan line (650) represents a portion of the frame (648)representing that image. Depending on the resolution, a particular frame(648) may include different numbers of scan lines (650) ranging fromless than a hundred to many hundreds.

To form a frame (648), a transducer (102), using beam forming circuitry,transmits and focuses pressure waves from different piezoelectricelements (FIG. 1, 104), for example, those in a particular column orcolumns (FIG. 5, 542) to a particular focal point. The reflected signalscollected by these piezoelectric elements (FIG. 1, 104) are received,delayed, weighted, and summed to form a scan line (650). The focal pointof interest is then changed to a different part of the frame, and theprocess is repeated until an entire frame (648), consisting of, forexample 100-200 scan lines (650), is generated.

While particular reference is made to a particular transmissiontechnique, many different transmit techniques may be employed, includingachieving multiple focus with a single transmission from multiplechannels. Moreover, the operations described in the presentspecification are also applicable to these multi-focal transmitsignaling techniques. Simultaneous multi-zone focusing can be achieved,for example, using chirp signaling and can help achieve betterresolution as a function of depth. As a specific example, chirpsignaling sends a coded signal during transmit where many cycles offrequency or phased modulated coded signals are transmitted. Thereceived echo is then processed with a matched filter to compress thereceived signal. This method has the advantage of coupling larger energyinto the target compared with situations when only 1 or 2 pulses aretransmitted. While axial resolution may become worse when transmittingmultiple signals, with chirp signaling, because of the matched filter inthe receiver, axial resolution is largely restored.

An issue with chirp signaling is that it uses many cycles of transmitpulses which can increase power output for transmit pulses of similaramplitude for all signaling cases. However, by electronically adjustingthe aperture in elevation, power output can be adjusted to allow varioustypes of signaling used in B-mode and Doppler imaging, where many morepulses are used.

FIG. 6B illustrates the azimuth axis, noted as direction xa. This is thesame as direction A-A in FIG. 6A, with lines (650) in FIG. 6A being inthe axial direction as shown in FIG. 6B and noted as za or depth in FIG.6B. FIG. 6B also notes the elevation direction ya. The elevationdirection may be particularly pertinent for 2D imaging. The ultrasonicbeam as shown is focused in an elevation plane (1201) to concentrate thebeam in a narrow direction and increase pressure in that plane at aspecific point in the axial direction. The beam is also focused in theazimuth plane (1202) in the in the azimuth direction.

If the azimuth focal point and the elevation focal point are relativelyat the same location, as shown in FIG. 6B, pressure at the target focalpoint increases. The ability to electronically control both elevationand azimuth focal points provides an operator to target any point in theelevation and axial dimension to create 3D focusing with increasedpressure at that point. Increases in pressure increase signalavailability to the transducer and also improves sensitivity. Further,if not focused in the elevation direction, the transmitted waveform canhit other objects away from the elevation plane (1201) and reflectedsignals from these unwanted targets would create clutter in the receivedimage. Note that FIG. 6B shows the acoustic beam travelling in depth inthe axial direction.

FIG. 6C illustrates various types of beam-reflecting elements arrangedon a column with different delays applied to each element on the column.For example, a first beam (4101) has equal delays to all elements thatcause waveforms to be delayed equally, resulting in a plane wavereferred to as a synchronous beam. Other examples include differentdelays applied to elements on a column to focus a beam at a point. For abeam focused at a point in the elevation plane, this is referred to assteering the beam or focusing and steering the beam. A second beam(4102) illustrates a focused beam. A third beam (4103) illustrates abeam with beam steering and a fourth beam (4104) illustrates a beam withsteering and focusing.

FIG. 6D illustrates an example of a transducer with 24 rows and 128columns, where each column includes 24 elements. Elements indicated bycircles in the columns share the same delay and are shaded, whereasother elements have different delays and are not shaded. Each column mayhave the same relative delay as elements of the other columns or eachcolumn may have different relative delays. The actual delay on anyelement is the summation of delay in the azimuth axis and in theelevation axis. Controls are implemented in an ASIC which creates pulsedrives to the elements with the appropriate delay in transmit mode andin receive mode.

In one example, the imaging device includes transmit elevation focusthat is achieved electronically. For example, electronic focus isachieved by changing relative delays of the beam transmitted by anelement on a column by an ASIC. Digital registers in the ASIC arecontrolled by an external controller, wherein a desired transmitelevation focal depth is sent to the ASIC. A desired azimuth focal depthis sent to the ASIC by an external controller wherein the ASIC setsrelative delay of elements. A desired azimuth focal depth is adjustedfor curvature in a transducer, ASIC, or board. Elevation focus isadjusted electronically to include delay adjustments to compensate forcurvature in the transducer. In another example, elevation focus istransmit elevation focus. Elevation focus also includes adjusting areceive elevation focus. A mechanical lens may be included that providesa fixed transmit and elevation focus, and wherein electronic elevationfocus allows further electronic change in the elevation focus. Unitspecific electronic adjustments of focal length of transducers may beused to enhance Doppler imaging sensitivity. Electronic adjustments mayinclude adjustment for unit to unit variations in curvature intransducers.

FIG. 7 illustrates the formation of a scan line (650), according to anexample of the principles described herein. A cross-sectional view ofone transducer (102) is taken along the line A-A from FIG. 6A andincludes the piezoelectric elements (104) that make up the transducer(102). In FIG. 7, just one piezoelectric element (104) of the transducer(102) is indicated with a reference number for simplicity. Moreover,note that the piezoelectric elements (104) depicted in FIG. 7 mayrepresent a top piezoelectric element (104) of a column (FIG. 5, 542)with other piezoelectric elements (104) extending into the page. FIG. 7also depicts circuitry that may be found in the controller (324) to forma scan line (650).

For simplicity, FIG. 7 only depicts seven piezoelectric elements (104),and seven respective columns (FIG. 5, 542). However, as described above,a transducer (102) may include any number of piezoelectric elements(104), for example, 128 columns (FIG. 5, 542), with each column (FIG. 5,542) having 32 piezoelectric elements (104) disposed therein.

To form a scan line (650), signals (752) are received from a number ofpiezoelectric elements (104), such as from each piezoelectric element(104) in a column (FIG. 5, 542). In some examples, signals forpiezoelectric elements (104) in a column (FIG. 5, 542) may be combinedinto a composite signal (754) which is passed to the controller (324).As each composite signal (754) is received at a different time due todifferent transmission lengths, the controller (324) delays eachcomposite signal (754) such that they are in phase. The controller (324)then combines the adjusted signals to form a scan line (650). Additionaldetail regarding the processing of received signals (754) by thecontroller (324) are presented in later figures.

As described above, a frame (FIG. 6A, 648) of an image is formed of manyscan lines (650), often 128 or more. These scan lines (650) cover thearea to be imaged. The time to collect and combine the scan lines (650)into a frame (FIG. 6A, 648) defines the quality of the video, in termsof the frame rate, of an object to be imaged. For example, assuming theexample of scanning a heart, and assuming the heart is 20 cm below thetransducer (102) surface, an ultrasound waveform takes approximately 130microseconds (us) to travel to the heart, assuming sound travels at 1540m/s in tissue. The signal is then reflected from the heart and takesanother 130 microseconds to reach the transducers (102) for a totaltransit time of 260 microseconds. Using N receive channels (FIG. 1,108), one scan line (650) is formed by transmitting from N transmitchannels (FIG. 1, 108) driving N columns (FIG. 5, 544) of piezoelectricelements (FIG. 1, 104) and receiving from all N columns (FIG. 5, 544)and processing the signals as indicated in FIG. 7. In an example, using128 channels, one scan line is formed by transmitting from 128 channels,driving 128 columns of piezoelectric elements and receiving from all 128columns and processing the signals. Assuming 128 scan lines (650) perframe (FIG. 6A, 648), the maximum frame rate is around 30 frames persecond (fps).

In some examples, 30 fps may be sufficient, for example, with livers andkidneys. However, to image moving organs, such as a heart, a higherframe rate may be desired. Accordingly, the imaging device (FIG. 1, 100)may implement parallel beamforming where multiple scan lines (650) canbe formed at the same time. As multiple scan lies (650) can be formed ata time, the effective frame rate may be increased. For example, if fourscan lines (650) could be formed at the same time, then the effectiveframe rate may go up to 120 fps. Parallel beamforming may be implementedin a field programmable gate array (FPGA) or graphical processing unit(GPU) (FIG. 3, 326) of the imaging device (FIG. 1, 100).

In some examples, parallel beam forming is used to initially increasethe frame rate, even if the rate is higher than needed. For example,with parallel beam forming, a frame rate of 120 fps may be achievable.However, if 30 fps is adequate, hardware such as transmit and receivechannels can be enabled for a portion of time, such as one fourth of thetime, cutting down power consumption by a factor of 4 or less. The timesaving takes into account some requirements that are not amenable tobeing completely shut down, but that can be placed into a materiallylower power state. For example, after a set of four scan lines aresimultaneously collected, the transmit (FIG. 1,106), receive channels(FIG. 1, 108) and portions of the control circuitry (FIG. 1, 109) may beturned off for a period of time, and then turned on again to collectanother four scan lines simultaneously.

Such techniques can reduce power consumption by larger factors, such asapproximately 3.3 times less than a starting power consumption value forthe example cited. In other words, parallel beam forming is employed toincrease the frame rate. This is followed by a selective shutdown ofcircuitry involved in creation of scan lines to reduce power, with theshutdown times such that targeted frame rates are still achieved. Thistechnique enables a reduction of power consumption compared withparallel beam formation not employing the circuitry. Such an operationdoes not affect the image quality as imaging artifacts can be digitallycorrected with operations that are not power intensive and can beexecuted in a display processor that is not located in the probe.Particularly, data from the imaging device (FIG. 1, 100) in the form ofscan lines (650) can be transported to the computing device (FIG. 2,216) unit using a USB interface and image processing can be done outsideof the imaging device (FIG. 1, 100) where there are less restrictions ontemperature rise. The amount of scaling is dependent upon the number ofparallel beams that are transmitted and received. For example, thescaling may be smaller when using two parallel beams or larger whenusing eight parallel beams.

FIG. 8 is a flowchart of a method (800) for selectively altering anumber of channels or number of elements per channel (FIG. 1, 106, 108)of an imaging device (FIG. 1, 100), according to an example of theprinciples described herein. According to the method (800), anindication is received (block 801) that power consumption or acousticpower output should be adjusted within the imaging device (FIG. 1, 100).The indication may come in a variety of forms. For example, if powerconsumption is to be reduced because temperature sensors indicate thattemperature is too high, an indication to reduce power may be sent tothe control circuitry. In another example, if the acoustic power outputis to be altered, an indication may be received by the control circuitryto alter the number of elements transmitting or power per element.

In an example, the imaging device (FIG. 1, 100) is first used to guidethe operator to obtain a medically relevant image by helping to orientthe imaging device (FIG. 1, 100) correctly. This may be accomplished byusing artificial intelligence techniques that leverage machine learningwith algorithms to guide the user to orient the image in the properorientation for the desired view of the organ (FIG. 2, 214) beingimaged. After the proper orientation is obtained, then the actualimaging session can start at a relevant resolution. However, during theorientation and guidance session, high resolution is not required andtherefore the imaging device (FIG. 1, 100) can be set to a lower powerand lower resolution mode, saving power for the overall imaging session.

FIG. 9 depicts a receive channel (108), according to an example of theprinciples described herein. The receive channel (108) is coupled to apiezoelectric element (FIG. 1, 104) to receive the reflected pressurewave (FIG. 2, 210). FIG. 9 also depicts the connection between thepiezoelectric element (FIG. 1, 104) and the transmit channel (FIG. 1,106). During a transmit operation, the transmit/receive switch is off,isolating the LNA (1056) from the drive signal on node A. In oneexample, after transmission is complete, the transmit channel (FIG. 1,106) pulse driver is set to a high impedance state to allow a pressuresignal to be received by the transducer during a receive operation atthe node (A in FIG. 9) where the received pressure signal is connectedto the LNA by a transmit/receive switch which is now turned on. Duringtransmit operations, the transmit pulse driver delivers a transmitsignal, also at node A, which the transducer converts to an ultrasonicpressure wave and transmits to the target being imaged.

In other words, the receive channel (108) receives a reflected pressurewaveform from the target to be imaged and the receive channel (108)converts the pressure to electrical voltage. Specifically, the reflectedpressure wave is converted to an electrical charge in the transducerwhich is converted to a voltage by an LNA. The LNA is a chargeamplifier, where charge is converted to an output voltage. In someexamples, the LNA has programmable gain, where the gain can be changedin real time and controlled by C_(f) and R_(f), where C_(f) and R_(f)are a bank of programmable components as shown in FIG. 11. An example ofan LNA (1056) with programmable gain is depicted in FIG. 10.

The LNA (1056) converts charge in the transducer to a voltage output andalso amplifies the received echo signal. A transmit/receive switchconnects the LNA (1056) to the transducer in the receive mode ofoperation.

The output of the LNA (1056) is then connected to other components tocondition the signal. For example, a programmable gain amplifier (PGA)(1058) further adjusts the magnitude of the voltage and provides a wayto change the gain as a function of time and may be known as a time gainamplifier. As the signal travels deeper into the tissue, it isattenuated. Accordingly, a larger gain is used to compensate, whichlarger gain is implemented by the TGC (time gain compensation). Thebandpass filter (1060) operates to filter out noise from band signals.An analog-to-digital converter (ADC) (1062) digitizes the analog signalto convert the signal to the digital domain such that further processingcan be done digitally. Data from the ADC (1062) is then digitallyprocessed at a demodulation unit (1064) and passed to the FPGA (326) togenerate the scan line (FIG. 6A, 650) as depicted in FIG. 7. In someimplementations, the demodulation unit (1064) can be implementedelsewhere, for example in the FPGA (326). The demodulation unit (1064)frequency-shifts the carrier signal to baseband with two components inquadrature (I and Q), for further digital processing. In some examples,the ADC (1062) may implement a successive-approximation-register (SAR)architecture to reduce latency of the ADC (1062). That is, as the ADC(1062) is turned off and on repeatedly, it needs to have little to nolatency so as to not delay signal processing following turning on.

FIG. 10 depicts a low-noise amplifier (LNA) (1056) of a receive channel(FIG. 1, 108), according to an example of the principles describedherein. A bank of capacitors C_(f1)-C_(fn) are electronically selectedby turning on switches M₁-M_(n) and are connected across an operationalamplifier (1166). R_(f1)-R_(fN) are a bank of resistors that are alsoelectronically selected by turning on switches S₁-S_(N). The signal gainis a ratio of the transducer capacitance C_(p) divided by feedbackcapacitance C_(f), where appropriate switches are turned on to connectC_(f) and R_(f) values from the bank as desired. A bias voltage (VBIAS)is used to provide a bias voltage such that the polarity of the fieldacross the transducer does not change as a signal swings in a positiveor negative manner on the opposite electrode of the transducer.

FIG. 10 also depicts a bias current input (IBIAS). IBIAS may begenerated by the circuit depicted in FIG. 11. BIAS is used to change thetransconductance of the LNA (1056), where a higher current level reducesnoise level. Additionally, a digital input indicating power down is usedto shut down the LNA (1056). To achieve fast power up, IBIAS needs to beestablished quickly with an example implementation shown in FIG. 11.

FIG. 11 illustrates a circuit diagram of a fast power-up biasing circuit(1268), according to an example of the principles described herein. Asdescribed above, when the receive channel (FIG. 1, 108) is powered onand off multiple times during operation, components can be rapidlyturned on and off in order to ensure proper dissipation of heat andproper operation of the imaging device (FIG. 1, 100). In this example,the IOUT terminal is coupled to the IBIAS of the LNA (FIG. 10, 1056) soas to ensure that the LNA (FIG. 10, 1056) is quickly powered up. Inorder to implement the imaging device (FIG. 1, 100) effectively, thecomponents in the signal path such as the LNA (FIG. 10, 1056) and theADC (FIG. 10, 1064) in each receive channel (FIG. 1, 108) are able toshut down in around hundreds of nanoseconds and also be powered up inaround 1 us. The fast power-up biasing circuit (1268) depicted in FIG.11 is one example of providing such a quick power-up and shutdown. Thebiasing circuit (1268) depicted in FIG. 11 exhibits fast turn on andturn off times. If the Power Down signal is high, then Power Upbootstrap is low, turning off switches S1-S3, so that they do notconduct current and reducing the value of IOUT so as to effectively turnit off. When Power Down goes to low, (i.e., it is desired to power upthe LNA (1056)), both inputs of the NOR gate are at low and this createsa high logic signal at Power Up bootstrap. This turns on the switchesS1-S3 and restores current to IOUT rapidly. IOUT provides a currentoutput whose value is copied in other circuits such as the LNA (FIG. 10,1056) to power these circuits. The value of IOUT is close to zero duringpower down and has a higher value, typically in the tens or hundreds ofμA, during power up.

FIGS. 12-16 illustrate the fabrication of a piezoelectric element (FIG.1, 104), according to an example of the principles described herein.FIG. 12 shows a top view of a membrane (1374) disposed on substratelayers (1370) and (1372). FIG. 13 shows a cross-sectional view of themembrane (1374) and substrate (1372), taken along the line B-B in FIG.12.

FIG. 14 illustrates a top view of a bottom electrode (1578) disposed ona substrate layer (1370) and arranged over the membrane (1374) accordingto an example of the principles described herein. FIG. 15 shows a topview of a piezoelectric layer (1680) disposed on the bottom electrode(FIG. 14, 1578) according to an example of the principles describedherein. In some examples, the piezoelectric layer (1680) may have asimilar projection area as the bottom electrode (1578) so that thepiezoelectric layer (1680) may cover the entire portion of the bottomelectrode (1578).

FIG. 16 illustrates a top view of a piezoelectric element according toan example of the principles described herein. As depicted, a topelectrode (1782) is disposed on the piezoelectric layer (1680) andarranged over the membrane (FIG. 13, 1374). In some examples, a topelectrode conductor (1783) may be disposed on and electrically coupledto the top electrode (1782), while bottom electrode conductors (1784-1)and (1784-2) may reach the bottom electrode (1578) through one or morevias (1790-1, 1790-2). In this example, the top electrode (1782), thepiezoelectric layer (1680) and the bottom electrode (1578) form a twoterminal piezoelectric element and the membrane (1374) vibrates when anelectrical voltage is applied across the top and bottom electrodes(1782, 1578). The electrical charge may be developed across the top andbottom electrodes (1782, 1578) when the membrane (1374) is deformed by apressure wave (FIG. 2, 210) during a receive mode/process.

The substrate (1372) may be thinned to obstruct cross talk betweenadjacent piezoelectric elements, where the thinner material does notsupport travel of the ultrasound waves in the substrate (1372) betweenactivated elements or sub-elements. FIGS. 17A-17B illustrate elementconstruction to achieve isolation and reduce cross talk betweenneighboring elements. The substrate (1372) may correspond to thetransceiver substrate (540) in FIG. 5. As depicted, a membrane (1374)may be formed on the substrate (1372) with a cavity (1376) (see FIG. 13)formed by removing a portion of the substrate (1372), to thereby formthe membrane (1374) that may vibrate relative to the substrate (1372) inthe vertical direction. The cavity (1376) may be formed by waferprocessing techniques, such as etching, for example, deep reactive ionetching (DRIE). The substrate (1372) may be formed of the same materialas the membrane (1374). In another example, the substrate (1372) may beformed of a different material from the membrane (1374). The cavity(1376) (see FIG. 13) may be formed after the other components, of thepiezoelectric element (FIG. 1, 104), are formed. While FIG. 13 andothers herein depict the membrane (1374) as having a circular projectionarea, the membrane (1374) may have other suitable geometrical shapes.

In particular, FIG. 17A illustrates the membrane (1374) formed onsubstrate (1372), where a cavity (1376) resides below the membrane(1374). The membrane (1374) is surrounded by substrate (1372) materialon all sides. FIG. 17B illustrates four membranes (1374) with substrate(1372) separating them. It may be desirable to isolate the piezoelectricelements (FIG. 1, 104) from each other to minimize cross talk. Crosstalk is the influence that a piezoelectric element (FIG. 1, 104) canhave on another piezoelectric element (FIG. 1, 104) through acoustic ormechanical or electrical coupling. Such coupling is generallyundesirable, as it makes each membrane (1374) less independent. In someexamples, piezoelectric elements (FIG. 1, 104) are separated by a grooveor trench (1373) cut in the substrate (1372) and that attenuates signalstravelling towards its neighbors as shown in FIG. 17B. The trench (1373)can be filled by air or be a vacuum. This presents a discontinuity inimpedance between adjacent areas and attenuates energy flowing from apiezoelectric element (FIG. 1, 104) towards its neighboringpiezoelectric element (FIG. 1, 104). It is understood that even if somediagrams do not show this trench, it is incorporated by reference perthis explanation.

FIG. 17C depicts transducer elements connected to electronics using twoconnection points labeled X and O. Transducer (1420) includes substrates(1411), membrane (1406), piezo material (1409), another material orcoating attached to transducer surface (1403), and electrodes (1407) and(1410). A first electrode (1407) is connected with wire (1408) to pillar(1402). Piezo material (1409) is disposed on electrode (1407). A secondelectrode (1410) is disposed on top of piezo material (1409) andconnected with a wire (1405) to pillar (1414). An ASIC (1417) is shownbelow the transducer (1420) and connected to the transducer (1420) bytwo pillars (1401) and (1415) for every element of the transducer(1420). Pillars (1401) and (1402) are connected to a common terminal ofelements known as X node, which is connected to a DC bias voltage. Thetransmit or receive terminal of the element is known as O node. Pillars(1414) and (1415) are attached to connect the transducer (1420) to theASIC O node. Pillars (1401) and (1402) are connected together tointegrate an element of transducer (1420) to related electronics in anASIC (1417).

Similarly, pillars (1414) and (1415) are connected together to integratean element of the transducer (1420) to related electronics in the ASIC(1417). The space between the transducer (1420) and the ASIC (1417) maybe air-filled or a vacuum. The surface of transducer (1420) facing theASIC (1417) may have a layer of coating (1403) to absorb or attenuateacoustic energy travelling in the direction of the ASIC (1417) from thetransducer (1420). Additionally, an acoustic absorber layer (1404) canbe attached below the ASIC (1417) as shown to absorb acoustic energytravelling from the transducer (1420) through the ASIC (1417). Theregion covering the substrate (1411) and membrane (1406) (i.e., in thecavity area and entire surface of the substrate 1411) is filled withimpedance matching material making up the interface between thetransducer (1420) and the target to be imaged. In some cases, thematerial under the membrane (1406) is made with a different acousticimpedance compared to material in the remaining part of the substrate(1411). This mismatch in impedance can also disrupt the possibleacoustic coupling between neighboring elements or sub-elements asacoustic energy travels through the impedance matching layer.

In some examples, the piezoelectric elements (FIG. 1, 104) have asuspended membrane associated with them that vibrates at a centerfrequency and several other frequencies when exposed to stimulus at thatfrequency and as such behave like resonators. There is a selectivityassociated with these resonators, known as a Q factor. For ultrasoundimaging devices (FIG. 1, 102), Q may be usually designed to be low(close to one) and achieved by a combination of design of the pixels andloading applied to the pixels in actual use. The loading may be providedby application of a layer of RTV or other material to the surface of thepiezoelectric elements (FIG. 1, 104), where the loading may alsofacilitate closer impedance matching between the transducer surfaceemitting and receiving the pressure waves and the human body part beingimaged. The low Q and the well-matched center frequency may allow theline element to essentially act like a line imaging element withsubstantially one center frequency. Loading may also include a matchinglayer below the transducers, where the emitted waveform is absorbed byan acoustic absorber.

FIG. 18 illustrates a schematic diagram of a piezoelectric element(1800), according to an example of the principles described herein. Apiezoelectric layer (1880) is disposed between a first electrode (1882)and a second electrode (1878). The first electrode (1882) may beconnected to a ground or a DC bias via a first conductor (1886) and thesecond electrode (1878) may be connected to an electrical circuit (notshown in FIG. 18) through a second conductor (1890).

In the conventional piezoelectric elements, the piezoelectric layer isthick, approaching around 100 μm and typically an AC voltage of +100 to−100 V across the piezoelectric layer is required to create anultrasonic pressure wave of sufficient strength to enable medicalimaging. The frequency of the AC drive signal is typically around theresonating frequency of the piezoelectric structure, and typically above1 MHz for medical imaging applications. In conventional systems, thepower dissipated in driving the piezoelectric element is proportional tof*C*V², where C is capacitance of the piezoelectric element, V is themaximum voltage across the piezoelectric layer, and f is frequency withwhich drive is being done. Typically, when transmitting pressure waves,multiple piezoelectric lines are driven together with somewhat differentphase delays to focus the pressure waves or to steer a propagationdirection of the pressure waves.

In the piezoelectric element (1800) of the present specification, thepiezoelectric layer (1880) may be much thinner, for example 1-5 μmthick. This large reduction in thickness enables the use of lowervoltage drive signals for the piezoelectric element (1800), where thevoltage is lowered approximately by the amount by which the thickness ofthe piezoelectric layer (1880) is lowered to maintain the similarelectric field strength. For example, the voltage potential across thetwo electrodes (1882) and (1878) may range from around 1.8 V to 40 Vpeak to peak. The capacitance of the piezoelectric element (1800) mayincrease due to the reduction in thickness of the piezoelectric layer(1880) for similar piezoelectric material. For instance, when the drivevoltage is decreased by a factor of 10 while the thickness of thepiezoelectric layer (1880) is also decreased by a factor of 10, thecapacitance increases by a factor of 10 and the power dissipationdecreases by a factor of 10. This reduction in power dissipation alsoreduces heat generation and temperature rise in the piezoelectricelement (1800). Thus, using lower drive voltages and thinnerpiezoelectric layers, compared to the conventional piezoelectricelements, power consumption is lowered and this also lowers temperatureof the piezoelectric element (1800) in operation.

FIG. 19A is a schematic diagram of a piezoelectric element (1900),according to another example of the principles described herein. FIG.19B shows a symbolic representation of the piezoelectric element (1900)in FIG. 19A. As depicted, the piezoelectric element (1900) is similar tothe piezoelectric element (1800), with the difference that thepiezoelectric element (1900) has more than two electrodes. Morespecifically, the piezoelectric element (1900) includes: a top electrode(1982), a first bottom electrode (1978-1); a second bottom electrode(1978-2); a piezoelectric layer (1980) disposed between the top andbottom electrodes; and three conductors (1984-1), (1984-2), (1984-3)that are electrically coupled to the top and bottom electrodes (1982),(1978-1), (1978-2), respectively. Hereinafter, the terms top and bottommerely refer to two opposite sides of the piezoelectric layer, i.e., thetop electrode is not necessarily disposed over the bottom electrode.

The piezoelectric element (1900) depicted in FIG. 19A is particularlyhelpful to increase sensitivity of transmit and receive operations. Forexample, when a piezo material is manufactured, the dipoles in the piezomaterial are not aligned and for optimal piezo performance, a polingprocess is implemented where a strong electric field is applied acrossthe piezo film at high temperature (such as 175° C.). This establishesthe direction of the electric field for later operations. However, if apiezo sub-element used for basic transmit and receive operation haspoling done in orthogonal directions, its sensitivity can be enhanced.For a receive pressure wave, the piezo sub-element forms more chargesignal on receive operations and for a given transmit voltage drive,more pressure is created.

The piezoelectric element (1900) in FIG. 19A includes 3 leads, where afirst lead (1984-1) can be grounded during a poling operation, a secondlead (1984-2) can be at a high voltage, say positive 15V, and a thirdlead (1984-3) can be at −15V. Accordingly, an orthogonal electric fieldis established in the sub-elements of piezoelectric element (1900)during this poling operation. During actual use, the second lead(1984-2) and third lead (1984-3) can be tied to DC bias voltages and actas a virtual ground while the first lead (1984-1) is used for transmitand receive operations.

While a unimorph piezoelectric element is shown in FIG. 19A purely forthe purpose of illustration, in embodiments, a multilayer piezoelectricelement composed of a plurality of piezoelectric sublayers andelectrodes can be utilized. In embodiments, the piezoelectric layer(1980) may include at least one of PZT, PZT-N, PMN-Pt, AlN, Sc—AlN, ZnO,PVDF, and LiNiO3.

FIG. 19B illustrates a symbolic representation of the piezoelectricelement of FIG. 19A, according to an example of the principles describedherein.

FIG. 19C illustrates a schematic cross-sectional view of a piezoelectricelement (1900), according to an example of the principles describedherein. The piezoelectric element (1900) may be disposed on a substratelayer (1970). Substrate layer (1972) along with substrate layer (1970)constitutes a substrate. A cavity (1976) may be formed in the substratelayer (1972) to define a membrane (1374). The membrane (1374) is theportion of the substrate layer (1970) that overlaps with the cavity(1976) with a shape similar to the cavity (1976). The substrate layers(1972) and (1970) may be made from the same material and moreover may beformed from a single continuous material.

The piezoelectric element (1900) may include a piezoelectric layer(1980) and a first electrode (1982) that is electrically connected to atop electrode conductor (1984-1). The top electrode conductor (1984-1)may be formed by depositing TiO₂ and metal layers on the membrane(1374).

A first bottom electrode (1978-1) may be grown above the piezoelectriclayer (1980) and electrically connected to a first bottom conductor(1984-2). A second bottom electrode (1978-2) may also be grown above thepiezoelectric layer (1980) and disposed adjacent to the second bottomconductor (1984-3) but be electrically isolated from the first bottomconductor (1984-2). The second bottom electrode (1978-2) and secondbottom conductor (1984-3) may be formed by depositing one metal layer onthe piezoelectric layer (1980) and patterning the metal layer. In someexamples, the projection areas of the electrodes (1984) may have anysuitable shape, such as square, rectangle, circle, ellipse, etc.

The first electrode (1982) may be electrically connected to theconductor (1984-1) using a metal, a via and interlayer dielectrics. Insome examples, the first electrode (1982) may be in direct contact withthe piezoelectric layer (1980). The second bottom conductor (1978-2) maybe deposited or grown on the other side of the piezoelectric layer(1980) with respect to the first electrode (1982).

FIG. 19D illustrates a schematic diagram of a piezoelectric element(1992), according to another example of the principles described herein.As depicted, the piezoelectric element (1992) includes two subpiezoelectric elements (also referred to as sub-elements) (1996-1) and(1996-2). Sub-elements (1996-1) and (1996-2) are contiguous, making thespace efficient.

Each sub-element (1996-1) and (1996-2) may include a two terminaldevice. For example, sub-element (1996-1) as shown includes one bottomelectrode (1982-1), one top electrode (1978-1), one membrane (1374-1),and one piezoelectric layer (1980-1) The designation of top or bottomdoes not physically designate that one is above another, but is used toindicate that electrodes are at different vertical locations and top andbottom is used interchangeably. The other sub-element (1996-2) has onebottom electrode (1982-2), one top electrode (1978-2), and onepiezoelectric layer (1980-2) (see Id.). Each sub-element (1996-1) and(1996-2) may be disposed on a respective separate membrane (1374-1) and(1374-2). Membranes (1374-1) and (1374-2) are separated by a solid area(1399) made of solid matter such as silicon dioxide. When sub-elements(1996-1) and (1996-2) are active, they can influence the behavior ofeach other or a neighboring sub-element. This can happen by transfer ofenergy from one sub-element to another sub-element or one element toanother element. Such transfer can take place, for example, byultrasonic waves travelling from sub-element (1996-1) to sub-element(1996-2) through the solid area (1399) or vice versa. It is beneficialto minimize such an interaction to minimize cross talk.

One example of reducing cross talk is via trenches such as trench (1997)shown in FIG. 19E. The trench (1997) can be air-filled or a vacuum (e.g,by incorporating a cover over the trench)). A trench may be used forsub-elements (1996-1) and (1996-2) in FIG. 19D to reflect cross talkcausing wavefronts to return. Further cross talk minimizing techniquesmay also be implemented. For example, an impedance matching layer (notshown) may be applied over the transducer surface and the solid area(1399) to cause them to have a different acoustic impedance compared tomaterial over membrane areas 1374. This disrupts acoustic wavestravelling from one sub-element to another through the acoustic mediumin the impedance matching layers.

Ultrasonic waveforms traveling in solids may reflect back from thetrenched areas and prevent or reduce forward propagation of the waveformin the trench areas. It should be apparent to those of ordinary skill inthe art that the conductors (like 1984-1, 1984-2, and 1984-3) may beconnected to respective electrodes (1978-1) and (1978-2), using metalsvia interlayer dielectrics (ILD), and so on, in a similar manner as thepiezoelectric element illustrated in FIGS. 12-16. For simplicity, allconductor connections are not shown.

Sub-elements (1996-1) and (1996-2) may further be employed for CWDoppler, where a transmit element continuously transmits while anotherelement continuously receives. A continuous transmit and receiveoperation helps the imaging technique not suffer from aliasing issuesthat accompany sampled Doppler methods, such as PW or color Doppler.Aliasing limits the maximum velocity of flow that can be reliablymeasured, to half of the pulse repetition frequency. Different regionsof the transducer are typically used for continuous transmit andcontinuous receive so that the elements are widely separated, minimizingcross talk.

In some examples, the sub-elements (1996-1) and (1996-2) as shown inFIG. 19D may have different center frequencies and when operatedtogether as a single composite element, exhibit wider bandwidth. Thesub-elements (1996-1) and (1996-2) still operate as a two-terminaldevice when the top terminal and bottom terminals of sub-elements(1996-1) and (1996-2) are connected together. This wide bandwidthperformance can also be achieved using the structure shown in FIG. 19C.Sensitivity in this structure can be further increased using dualpolarization techniques.

FIG. 19E illustrates a representative example of an imaging device whereone sub-element (2997-1) is configured to be continuously in transmitmode and another sub-element (2997-2) is configured to be continuouslyin receive mode. The imaging device includes a first top electrode(1982-1) and second top electrode (1982-2), first bottom electrode(1978-1) and second bottom electrode (1978-2); piezoelectric layer(1980-1) disposed between top electrode (1982-1) and bottom electrode(1978-1); piezoelectric layer (1980-2) disposed between top electrode(1982-2) and bottom electrode (1978-2); and two conductors (1984-1) and(1984-2) that are electrically coupled to respective top and bottomelectrodes (1982-1),(1978-1) and (1982-2),(1978-2). Hereinafter, theterms top and bottom merely refer to two opposite sides of thepiezoelectric layer.

A trench (1998) is provided between the membrane (1374-1) of sub-element(2997-1) and membrane (1374-2) of sub-element (2997-2) to minimize crosstalk between sub-elements (2997-1) and (2997-2). In one example, CWDoppler imaging can be performed using one of the sub-elements (2997-1)for transmit and another of the sub-elements (2997-2) for receive. Thisallows efficient utilization of the aperture size (FIG. 21, 3412), wheretransmitting and receiving elements can be adjacent. When CW Dopplerimaging is performed by programming an element to be in transmit mode ofoperation continuously while another element in a different portion ofthe imager is programmed to be continuously in receive mode, cross talkfrom the two elements are relatively small compared to other types ofnoise, since they are spatially separated by relatively large distancesin relation to the dimensions of the transducer. For PW operations, thesame sub-element can be used for transmit and then switched to receivemode.

FIG. 19F shows an example of reducing cross talk between neighboringelements. In this example, membranes 2905-1, -2 are electricallysimulated by electrodes (FIG. 19E, 1982-1, -2 and 1978-1, -2), whichcauses an ultrasonic waveform to be transmitted in the direction of area2902-1 and 2902-2. Wavefronts 2901-1, -2 traveling sideways arereflected and attenuated by trenches 2998-1, -2, -3. Areas 2903-1, -2,-3 represent materials intended to match impedance of transducers totissue. Areas 2903-1, -2, -3 have a different impedance than areas2902-1, -2. Therefore, wavefronts 2901-1, -2 traveling sideways arereflected by the mismatch and become attenuated, which reduces crosstalk. Materials may be mismatched, for example, by applying an acousticlensing layer over the bottom surface of one or more areas 2903-1, -2,-3 and 2902-1, -2. In some embodiments, materials in one or more areas2903-1, -2, -3 and areas 2902-1, -2 are kept the same.

FIG. 19G shows an example of reducing cross talk between neighboringelements. In this example, multiple trenches 3998-1, -2, -3, and 3999-1,-2, -3 are utilized to isolate coupling between adjacent elements orsub-elements and thereby provide crosstalk isolation. Trenches 3998-1,-2, -3 start from opposite sides of trenches 3999-1, -2, -3 on thesubstrate 3002. A first trench (3998-1) starts from a top surface, whilea second trench (3999-1) starts from a bottom surface. Similarly, othertrenches (3998-2, 3999-3) start from the top surfaces and still moretrenches (3999-2,3993-3) start from the bottom surface. Connections(3000-1, 3000-2, 3000-3) establish an electrical connection between acontroller (3200) such as an ASIC and the structure (3300) containingthe vibrating membrane, which structure may be amicro-electro-mechanical system (MEMS) structure. The double trencharrangement isolates any vibration energy transmitted from thecontroller (3200) via the connections (3000-1, 3000-2, 3000-3) and thentransferred to an adjacent element, as shown by (3001), indicatingreduced vibration coupling for elements with cavities (3901-1, 3901-3).In general, two trenches provide improved isolation, compared to onetrench. Such a topology may be referred to as front firing, where thecavities (3901-1, 3901-3) are facing the ASIC controller (3200). In someexamples a connection (3000-2) supports membrane (3905-2). Note that thediagram is not drawn to scale and is intended to illustrate theprinciple of operation.

In one example, an ASIC is attached to the substrate and connectedelectrically to enable anatomy and doppler flow imaging, where eachpiezoelectric element exhibits a plurality of modes of vibration.Imaging may be performed by the transducer at low frequencies such asfor abdominal or cardiac imaging or at higher frequencies formusculoskeletal (MSK) or vascular imaging.

In one example, the membrane is connected to the ASIC in a back firingorientation in which the cavity faces the imaging target. In anotherexample, the membrane is connected to the ASIC in a front firingorientation, where the cavity faces the ASIC and the membrane emits andreceives from the front face.

In another example, the imaging device includes MEMS-based elements thathave wide bandwidth. The imaging performed by the transducer may be forlow frequency imaging, such abdominal or cardiac imaging, or highfrequency imaging, such as musculoskeletal (MSK) or vascular imaging.

In another example, the imaging device further includes MEMS-basedelements that have wide bandwidth. The imaging may be performed by thetransducer for low frequency imaging for abdominal or cardiac imaging orhigh frequency imaging (MSK) or vascular imaging.

FIG. 19H shows an example of reducing cross talk between neighboringelements. Compared to FIG. 19G, the orientation of the vibratingmembrane is flipped. The orientation of FIG. 19G is referred to as frontfiring, whereas the orientation of FIG. 19H is referred to asbackfiring. In this example, the cavities (3901-1, 3901-2) faces awayfrom the ASIC controller (3200) and instead face the target to beimaged. In this example, the connections (3000-1, 3000-2, and 3000-3)that connect to the ASIC controller (3200) can be made without using TSV(through silicon via) because metallization and connection on the MEMSstructure (3300) are within a few micrometers away from each other andmetal vias and other connections that do not require TSVs. TSVs aredifficult to manufacture and introduce increased cost and complexitiesin the manufacturing process. In the backfiring topology depicted inFIG. 19H, the trenches (3999-1, 3999-2, and 3999-3) start from thebottom surface of the MEMS structure 93300), while other trenches(3998-1, 3998-2, and 3998-3) start from the top surface to theconnections (3000-1, 3000-2, and 3000-3). As described above, the use oftwo trenches (3998-2 and 3999-2) and similar structures on the otherside of the connection (3000-2) helps provide additional isolationbetween the membranes (3905-1 and 3905-2) as indicated by coupling(3001). The coupling (3001) is shown from the side facing the target tobe imaged. However, coupling from the ASIC controller (3200) side asshown in FIG. 19G also applies for FIG. 19H, since the double trencheshelp isolate coupling between adjacent membranes from the front face orthe back face of the MEMS structure (3300).

Although two trenches (3998-2 and 3999-2) are shown, a single trench maybe used. For example, a trench associated with the top surface, such astrench (3998-2) may be used alone or a trench associated with the bottomsurface like trench (3999-2). A single trench either from the top orfrom the bottom may also be sufficient to provide isolation for otherapplications described herein.

FIG. 19I illustrates a cross-sectional view of a piezoelectric element(1923) according to an example of the principles described herein. Asdepicted, the piezoelectric element (1923) may utilize a transverse modeof operation and include substrates (1925-1, -2), a membrane (1927)secured to the substrate at one end, a bottom electrode (1929) that iselectrically coupled to a conductor (1931), a piezoelectric layer(1933), and a top electrode (1935) that is electrically coupled to aconductor (1937). The membrane (1927) may be secured to the substrates(1925-1, -2) at one end so as to vibrate in the transverse mode. Themembrane (1927) can be supported on both sides with the substrates(1925-1, -2). It is to be noted that all previous examples of piezoelements can be operated in the transverse mode of operation and allsides of the membrane (1927) can be supported on the substrate.Transverse mode of operation and its principles apply to all examplesdiscussed herein.

It is noted that the piezoelectric element (1923) may have any suitablenumber of top electrodes. Also, it is noted that more than onepiezoelectric element may be installed on the membrane (1927). It isfurther noted that the substrates (1925-1, -2) and membrane (1927) maybe formed of one monolithic body and the membrane (1927) may be formedby etching the substrates (1925-1, -2).

Color Doppler flow mapping uses multi-gated sampling of many scan linesusing bursts of several cycles of waveforms at a carrier frequency thatthe transducer is responsive to. FIG. 20A illustrates several pulses2102-1, 2102-2, 2102-3, and 2102-4 that make up an ensemble. Each pulseconsists of at least one or multiple cycles at a carrier frequencytypically between 2-10 MHz.

FIG. 20B shows a color window (2110) inside a frame (2108) of atransducer 2100. Several scan lines (2104) are shown, each withmulti-gated pulses. Consecutive sampling of the signals along the scanline (2104) is timed according to the depth of the sampling location.Each returning echo is referenced to its range gate, which identifies itwith the spatial location of its origin and is electronically processedwith suitable delays. After all the echoes from the first pulse arereceived, a second pulse is launched in phase with the 1^(st) pulse on asame scan line (2104). Appropriate timing of the pulse repetitionfrequency is important in that a pulse must return before another pulsegoes out, otherwise range ambiguity is created. Once sampling of a scanline is completed, the next scan line is done in the same manner and acolor flow map is completed by multiple scan lines sweeping across thecolor window used.

To determine a mean Doppler shift, each echo from each pulse from aparticular range gate is compared to its previously sampled pulse fromthe same range gate. An auto correlation technique is used to obtain themean Doppler phase shift. Auto correlation is achieved delaying echosamples appropriately with respect to previous similar echoes from thesame line, multiplying and integrating results. Auto correlators measurephase difference from two consecutive echoes. Static portions of thetarget (i.e., not flow related) do not show phase differences, but phasefrom items that are moving, like blood, will show a difference.

Doppler imaging is sensitive to noise. Gain control can be used forsignal amplification. Separate controls can be designed for pulse echoimaging and for color Doppler function. Larger gains in color Dopplermake the imaging more sensitive. However, an increase in gain alsoincreases noise from physical components in the imager. A key componentof this noise comes from the LNA of the receiver and so it may bedesirable to achieve a very low noise floor for these LNAs. Because lownoise floor causes high power consumption and thermal heating in thetransducer, LNAs in the imager may be designed to be active only in acolor flow window activated, with other LNAs in the imagers placed in alow power state. Further, the active LNAs may be electronicallyadjustable to optimize according to power vs noise level performanceneeded.

A high pass filter may be used to eliminate high amplitude low frequencyDoppler shift signals generated by movements of vascular walls, movingtissue, and heart movements. These signals have high power content thatcan corrupt lower level signals from, for example, blood flow. A highpass filter blocks low frequency information from these spurious movingstructures. However, it can also block low velocity blood flow signalspresent in certain target types but not in others. Therefore, anyhardware-based filter also needs to be programmable with respect tocutoff frequency. This minimum level of filtering is then augmented withwall filters that are implemented in software. The wall filters haveadjustable levels of thresholds in the high pass function andsophisticated ability to discriminate between low velocity blood flowand wall motion. They are also responsive to different applications,frequency used, and pulse repetition rates. In an exemplary embodiment,a programmable high pass function is built in to the imaging head aroundthe LNA. This allows a high pass filter functionality with remaininghigh pass functions to be implemented in a wall filter later in thesignal chain.

Doppler shifts are sensitive to the angle of insonation of the flow axisand the ultra sound beam (see equations above). The signal can alsocompletely disappear if the angle is zero (see equations above). Theangle can be improved by moving the probe physically when possible.However, in an exemplary embodiment, the scan lines can be also beelectronically steered in 2D or 3D, when a 2D matrix of elements areused, with each element having independent control on Tx and Rxfunctions, including time delay. Thus, the desired angle can beelectronically achieved by steering the beam to the desired location. Insuch an arrangement, each element can be selected electronicallyindependent of neighboring, or adjacent elements and independentlyplaced in Tx or Rx modes and appropriate timing delays can be applied toelements whether in Tx or Rx mode.

As noted, Doppler imaging is sensitive to noise and signal-to-noiseratio. It is therefore desirable to increase the signal in instancesdescribed herein. Traditionally, 2D imagers used a mechanical lens witha curvature in the elevation direction to focus energy in the elevationplane. This resulted in pressure in the elevation focal point andenhanced sensitivity. However, such a configuration results in a fixedfocal length that cannot be adjusted. In an example of the presentdisclosure, electronic focusing is implemented for 2D imaging using a 2Darray of elements. Additionally, a mechanical lens is retained. Theelectronic capability using a 2D array allows electronic changes in thefocal point and also allows focusing in three-dimensional space. Thesteering capability depicted above in FIG. 6C allows the beam to besteered to further improve Doppler sensitivity as noted earlier.Electronic focus in the elevation plane can also be implemented byapplying different relative delays for elements on a column. Forexample, in FIG. 5, elements 104 are arranged in rows and columns, wherereference number 542 indicates a column. Delays in the transmit drivesignal to each of these elements relative to each other creates focuspatterns or beam steering as shown in FIG. 6C.

Furthermore, transducer elements may be on a curved plane as shown inFIG. 4. This curvature may be intentionally created or may beinadvertently created due to stresses in the board on which thetransducer and ASIC are mounted or due to stresses in the transducerintegration with the ASIC. This can vary from unit to unit. Apredetermined focal point that is same for all devices would createerrors in actual focal point achieved due to the curvature. However, itis possible to measure the curvature of each unit on a production line.This information is then used to apply relative delays to the elementsthat compensate for these delays. An external controller sends thedesired delay information to the ASIC. The ASIC applies the compensateddelay to each element and restores high signal pressure output that wasdegraded by uncompensated curvature in the transducer elements.

In one example, the transducer may be a wide bandwidth multimodaldevice, where the membranes can vibrate at a number of differentfrequencies simultaneously spread over a wide band, thus creating a widebandwidth transducer. This operation is valid in both the transmit modeand the receive mode. This allows B-mode anatomy as well as flow basedon Doppler imaging to be possible over a wide bandwidth, and allows manyapplications (typically requiring separate imagers that cover a limitedbandwidth range) using the same imager.

While a piezoelectric element can exhibit multiple modes of vibration,in some examples, just one mode of vibration is triggered when inputstimulus is bandlimited to be less than frequencies of adjacent modes.Further, frequencies generated from a first mode of vibration can bedesigned to overlap those from the second mode of vibration. Stillfurther, in some examples, multiple modes of vibration occursimultaneously when driven by a wide band frequency input that includescenter frequencies.

In summary, an imaging device is described utilizing an array ofPMUT-based transducers connected to control electronics on a per elementbasis and housed in a portable housing. The imaging device allows systemconfigurability and adaptability in real time to actively control powerconsumption, temperature and acoustic power in the imaging device. Beamsteering in 3D space is also achieved. Elements can be programmed to bein receive or transmit mode. Electronics to enable B-mode anatomyimaging and Doppler mode flow imaging are enabled over a largebandwidth, typically relying on multiple transducers using conventionalbulk piezo imaging.

Another exemplary imaging device includes at least one piezoelectrictransducer. A transducer imaging device includes at least onepiezoelectric element. A two-dimensional (2D) array of piezoelectricelements is arranged in rows and columns on the piezoelectrictransducer. Each piezoelectric element includes at least two terminals.Each piezoelectric element may be physically isolated from each adjacentpiezoelectric element to reduce cross talk. A first column of thepiezoelectric elements includes each respective piezoelectric elementhaving a first top electrode programmed to be connected to a respectivereceive amplifier. A second column of the piezoelectric elementsincludes each respective piezoelectric element programmed to beconnected to a respective transmit driver. Each of the respectivepiezoelectric elements in the first column can be electronicallyprogrammed to be as if connected together to form a column. Each of therespective piezoelectric elements in the second set can beelectronically programmed to be as if connected together to form acolumn. Furthermore, any number of adjacent columns may be programmed tooperate in receive mode while a different number of columns locatedelsewhere maybe programmed to be in transmit mode. In some examples,multiple modes of vibration may be exhibited in each piezoelectricelement. A single receive amplifier may be used, where at least onepiezoelectric element in the first column is connected to the receiveamplifier. Also, a single transmit driver may be present where at leastone of the piezoelectric elements in the second column is connected tothe transmit driver. The electronically programmed connections of thepiezoelectric elements may enable connection of an arbitrary number ofpiezoelectric elements in a column.

In some examples, at least one sub-aperture may include at least onecolumn of piezoelectric elements and each piezoelectric element mayinclude two sub-elements. Each sub-element may be selected to operatewith a programmable transmit and receive function such that a firstsub-element can simultaneously transmit while a second sub-element isreceiving, and each sub-element can switch between a transmit mode and areceive mode. At least one piezoelectric element may comprise twosub-elements and two terminals, each sub-element having a differentcenter frequency and bandwidth such that when they are used in parallel,the piezoelectric element exhibits a wider bandwidth than any onesub-element by itself. In one example, at least one piezoelectricelement is used for B-mode and Doppler flow measurements. In an example,each piezoelectric element comprises two sub-elements used for CWDoppler imaging, and at least a first piezoelectric element is placed intransmit mode while a second piezoelectric element is simultaneouslyplaced in receive mode.

Connections of the piezoelectric elements in at least one of the columnsand rows are electronically programmable to enable connection of anarbitrary number of piezoelectric elements in the column and row.

A first piezoelectric element of an array may be continuously intransmit mode while a second piezoelectric element of the array iscontinuously in receive mode to enable continuous wave (CW) Dopplerimaging. A set of columns can transmit continuously while a set ofcolumns can be programmed to be in receive mode which also enables CWDoppler imaging. Regions may be separate to minimize cross talk betweenthe transmit and receive portions of the transducer array. The height ofthe columns, and specifically, the number of piezoelectric elements thatmake up a column, is electronically adjusted to adjust acoustic poweroutput, among other things. Thus, acoustic output power is adjusted byelectronically adjusting the number of elements participating in thetransmission. The power supply can be identical for Doppler based flowimaging and anatomy imaging. However, Doppler imaging involves many morepulses than say B-mode imaging. Therefore, more acoustic power output isdeveloped during flow imaging under similar conditions compared toB-mode, that may exceed regulatory limits. By electronically adjustingthe number of elements that contribute to acoustic power, the acousticpower output for flow imaging can be optimized. Additionally, the pulseamplitude developed at each element can be electronically selected,while using same power supplies for all imaging modes. This allowsacoustic power adjustment as needed as well as a low cost, low sizepower management circuit to power circuits for flow and anatomy imaging.This is helpful for low cost portable imagers. In an example, a samenumber of power supplies are used for Doppler modes and B-mode byelectronically adjusting acoustic power transmitted from at least aportion of the array of piezoelectric elements. In an example, powerfrom each piezoelectric element is adjusted by using appropriate levelsof a multilevel transmit pulsar output. In an example, the B-modes andDoppler modes maintain a specific power level, such as an acoustic powerlevel, and a specific mechanical index while using same power suppliesfor imaging modes.

In each of the examples, each piezoelectric element is used as if itwere connected to a transmit and receive channel to perform actionsdescribed in the specification. The channels may be in a constant statewhere they remain as a transmitting, receiving, or both transmitting andreceiving channel. Alternatively, there may be a changing state wherethe channels change between one of the types of states of transmitting,receiving, and both transmitting and receiving.

In addition, each piezoelectric element within the separate independentarray may exhibit one or more modes of vibration. In an example, amembrane supports multiple modes of vibration, enabling a largerbandwidth for the imaging device. An example includes that at least onepiezoelectric element comprises two sub-elements and two terminals. Eachsub-element has a different center frequency and bandwidth such thatwhen used in parallel exhibits a wider bandwidth than any onesub-element by itself. Anatomy and Doppler imaging is performed over alarge bandwidth with electronic steering and focus control of theelevation plane to improve sensitivity.

An example further includes that each piezoelectric element exhibitsmultiple modes of vibration, thus enabling Anatomy and Doppler imagingover a large bandwidth with electronic steering and focus control ofelevation plane. imaging may be performed by the transducer for lowfrequency imaging for abdominal or cardiac imaging. Also, imaging may beperformed by the transducer for high frequency imaging formusculoskeletal (MSK) or vascular imaging.

As described earlier, transducers may have a large imaging surface, oraperture, and it may be desirable to operate on the entire aperture. Anentire aperture relies on the entire array of elements or sub-elements.Under electronic control, the aperture size can be changed to include asmaller number of elements or sub-elements, and possibly down to asingle sub-element. A smaller aperture is a smaller imaging surface, orsubaperture, and includes a subset of piezoelectric elements in thepiezoelectric layer.

Turning to FIG. 21, an imaging device (3408) is shown with a transmitoperation (3409) and a receive operation (3410) as indicated by arrows.The solid arrows in the transmit operation (3409) and receive operation(3410) indicate sub-elements and subsets of piezoelectric elements (FIG.1, 104) being used in the operations in the area of the arrows. Thedotted arrows indicate which sub-elements and subsets of piezoelectricelements (FIG. 1, 104) are not being used. The aperture size (3412)indicates the portion of the imaging object (3415) that will be imagedas a result of the sub-elements and subsets being used. The selectionand configuration of sub-elements and subsets may be alteredelectronically to define the aperture size (3412).

Note that certain sub-elements may be used for one operation (e.g.,transmit, receive) while other sub-elements may be used for anotheroperation (e.g., transmit, receive). There may be some overlap in thesub-elements used for each operation. The sub-elements may be the samefor each operation. The sub-elements may further have simultaneoustransmit and receive capability.

Two sub-elements can also be used to further broaden bandwidth, wherecenter frequency of the sub-elements are different and when usedtogether simultaneously, broaden bandwidth when used in transmit orreceive operations. The imaging device may be implemented with multiplesub-elements such that a bandwidth of the multiple sub-elements combinedis larger than each sub-element.

Various types of imaging can be performed using the array ofpiezoelectric elements (FIG. 1, 104). For example, A scan, B scan, Cscan, and Doppler mode may be performed. Further types of imaging thatcan be performed include pulsed Doppler and color Doppler. Additionally,Doppler processing can be performed in which some clutter rejectionfiltering, such as programmable high pass filtering, occurs prior todigitizing, thus increasing a dynamic range of the Doppler signals withhigh levels of clutter. In an example, Doppler processing is performedon a Doppler signal received from at least one piezoelectric element anda low noise amplifier performs programmable high pass filtering on thereceived Doppler signal prior to digitization, and pay perform furtherdigital signal processing, and beam forming.

In some examples, an elevation plane may be tilted and focusedelectronically to get closer to an optimal Doppler angle for bettersignal visualization. FIG. 22 depicts an elevation angle (3604) definedby elevation plane (3602) between a horizontal plane (3608) and a lineof sight measured in a vertical plane. The imaging object (3606) canhave better visualization depending on the elevation angle (3604) thatmay be modified to obtain a desired visualization.

High quality Doppler imaging may have a high signal to noise ratio(SNR). The SNR is a function of the elevation angle (3604) shown in FIG.22. In an example, the elevation angle (3604) can be electronicallyadjusted for flow imaging. The elevation focus can be steered in theelevation plane (3602) by adjusting delays on elements on a column. Notethat focusing beams in the axial direction is controlled by adjustingdelays on elements in the azimuth direction. With independent delaycontrol in elevation and azimuth, 3D beam steering is possible toimproving Doppler signal amplitude. In an example, a steering structureis used for beam steering capability in 3D space. In another example, asteering structure is used for beam steering in 3D space electronicallyto get closer to an optimal Doppler angle for better signalvisualization. In another example, an azimuth focus, elevation focus,and an aperture size of the imaging device are to be alteredelectronically.

As shown in FIG. 23, the azimuth angle (3605) of an imaging device(3610) may vary to produce a circular sector field of view that spans asmuch as 90 degrees in an azimuth angle. This may be accomplishedsimultaneously or independently of the aperture size (FIG. 21, 3412)being altered. It is therefore possible to steer a transmit beam in 3Dspace and anatomy and flow imaging can be carried out in 3D space.

Elements and sub-elements of columns may be treated as separate,independent columns. Elements and sub-elements of rows may be treated asseparate, independent rows. In some variations, columns and rows, orportions thereof, switch roles so that they are treated as rows andcolumns, respectively.

Further configurations may include that the respective receiveamplifiers or single receive amplifier be enabled in a receive mode anddisabled in a transmit mode, used for example, in B-mode anatomyimaging, Color Doppler, or PW flow imaging. Similarly, configurationsinclude that the respective transmit drivers or single transmit driverbe enabled in a transmit mode and disabled in a receive mode for theimaging modes mentioned for receive amplifiers. An example includes thateach piezoelectric element is first placed into transmit mode andsubsequently placed into receive mode to receive echoes from thetransmit mode, wherein transmit power level, an azimuth focus, elevationfocus, beam steering in 2D or 3D space, and an aperture size of theimaging device are altered electronically.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

For purposes of explanation, specific details set forth herein are toprovide an understanding of the disclosure. It will be apparent,however, to one skilled in the art that the disclosure can be practicedwithout these details. Furthermore, one skilled in the art willrecognize that examples of the present disclosure may be implemented ina variety of ways, such as a process, an apparatus, a system, a device,or a method on a tangible computer-readable medium.

One skilled in the art shall recognize: (1) that certain fabricationsteps may optionally be performed; (2) that steps may not be limited tothe specific order set forth herein; and (3) that certain steps may beperformed in different orders, including being done contemporaneously.

Elements/components shown in diagrams are illustrative of exemplaryembodiments of the disclosure and are meant to avoid obscuring thedisclosure. Reference in the specification to “one example,” “preferredexample,” “an example,” or “examples” means that a particular feature,structure, characteristic, or function described in connection with theexample is included in at least one example of the disclosure and may bein more than one example. The appearances of the phrases “in oneexample,” “in an example,” or “in examples” in various places in thespecification are not necessarily all referring to the same example orexamples. The terms “include,” “including,” “comprise,” and “comprising”are understood to be open terms and any lists are examples and not meantto be limited to the listed items. Any headings used herein are fororganizational purposes only and shall not be used to limit the scope ofthe description or the claims. Furthermore, the use of certain terms invarious places in the specification is for illustration and should notbe construed as limiting.

1. A portable imaging device comprising: a portable housing; an application specific integrated circuit (ASIC) within the housing; a transducer within the housing, the transducer comprising an array of piezoelectric elements formed on a substrate, each piezoelectric element comprising: at least one membrane suspended from the substrate; at least one bottom electrode disposed on the membrane; at least one piezoelectric layer disposed on the bottom electrode; and at least one top electrode disposed on the at least one piezoelectric layer, wherein adjacent piezoelectric elements are isolated acoustically from each other, and a controller connectively coupled to the ASIC, wherein the controller is to implement an imaging mode by: selecting a predetermined first plurality of piezoelectric elements from the array of piezoelectric elements to transmit signals to form a transmit channel associated with the imaging mode; selecting a predetermined second plurality of piezoelectric elements from the array of piezoelectric elements to receive signals to form a receive channel associated with the imaging mode; and forming a frame from a plurality of scan lines obtained with the imaging mode, and wherein the imaging mode remains same or is switched to a different mode after the frame is completed.
 2. The imaging device of claim 1, wherein isolation between piezoelectric elements is achieved by at least one trench positioned between piezoelectric elements to isolate interaction between piezoelectric elements.
 3. The imaging device of claim 2, wherein isolation between piezoelectric elements is achieved by use of an impedance matching material that covers the substrate and membrane, a material under the membrane being made with a different acoustic impedance compared to a material in the remaining part of the substrate.
 4. The imaging device of claim 1, wherein the substrate is thinned to obstruct cross talk between adjacent piezoelectric elements.
 5. The imaging device of claim 1, further comprising: a backing layer disposed on a surface of the transducer facing the ASIC.
 6. The imaging device of claim 1, wherein each piezoelectric element exhibits a plurality of modes of vibration.
 7. The imaging device of claim 1, wherein each piezoelectric element is first placed into transmit mode and subsequently placed into receive mode to receive echoes from the transmit mode.
 8. The imaging device of claim 1, wherein a first piezoelectric element of the array is continuously in transmit mode while a second piezoelectric element of the array is continuously in receive mode to enable continuous wave (CW) Doppler imaging.
 9. The imaging device of claim 1, wherein the imaging mode is at least one of an A scan, B scan, C scan, or Doppler imaging.
 10. The imaging device of claim 9, wherein a same number of power supplies are used for the Doppler modes and B-modes by electronically adjusting acoustic power transmitted from at least a portion of the array of piezoelectric elements.
 11. The imaging device of claim 10, wherein power from each piezoelectric element is adjusted by using appropriate levels of a multilevel transmit pulsar output.
 12. The imaging device of claim 11, where acoustic output power is adjusted by electronically adjusting the number of elements participating in the transmission.
 13. The imaging device of claim 9, wherein the B-modes and Doppler modes maintain a specific acoustic power level and a specific mechanical index while using same power supplies for imaging modes.
 14. The imaging device of claim 1, further comprising steering structure for beam steering capability in 3D space.
 15. The imaging device of claim 1, further comprising steering structure for beam steering in 3D space to optimize a Doppler angle for better signal visualization.
 16. The imaging device of claim 1, wherein at least one piezoelectric element includes at least two sub-elements that are enabled such that a first sub-element can transmit while a second sub-element can receive.
 17. The imaging device of claim 1, further comprising circuitry to alter one or more of azimuth focus, elevation focus, or aperture size of the imaging device.
 18. (canceled)
 19. An imaging device, comprising: a transducer; a 2D array of piezoelectric elements arranged in rows and columns on the transducer, each piezoelectric element having at least two terminals, at least a first column of the piezoelectric elements, each piezoelectric element having a first top electrode connected to a respective receive amplifier or a transmit driver under programmed control, and at least a second column of the piezoelectric elements, each piezoelectric element having a first top electrode connected to a respective receive amplifier or a transmit driver under programmed control, the piezoelectric elements having sub-elements to be programmed either to transmit and then subsequently receive or programmed to simultaneously transmit and receive; and at least two trenches, each trench located on opposite sides of the substrate and configured to provide crosstalk isolation.
 20. (canceled)
 21. A method of imaging, comprising: selecting a first plurality of piezoelectric elements and a second plurality of piezoelectric elements form a two-dimensional (2D) array of piezoelectric elements within a housing, the piezoelectric elements arranged in rows and columns, wherein each piezoelectric element is interconnected with an application specific integrated circuit (ASIC) that is housed adjacent the piezoelectric elements to control various imaging modes in a portable imaging device, wherein: piezoelectric elements in a first column of the array comprise a first top electrode connected to a respective receive amplifier, each of the piezoelectric elements to be electronically programmed as if connected together to form a first column, and piezoelectric elements in a second column of the array comprise a second top electrode connected to a respective transmit driver, each of the piezoelectric elements to be electronically programmed as if connected together to form a second column; performing ultrasonic imaging by: transmitting signals with the first plurality of piezoelectric elements; receiving signals with the second plurality of piezoelectric elements; adjusting the received signals such that the received signals are in phase; forming a scan line from the received signals; forming a frame from a plurality of scan lines obtained during ultrasonic imaging wherein the frame is one of an imaging mode of an A scan, B scan, C scan, or Doppler imaging, and an imaging mode remains the same or is switched to a different imaging mode after the frame is completed. 